{"id":2009,"date":"2026-09-11T10:31:08","date_gmt":"2026-09-11T10:31:08","guid":{"rendered":"https:\/\/metaboliboost.com\/articles\/?p=2009"},"modified":"2026-09-25T13:29:08","modified_gmt":"2026-09-25T13:29:08","slug":"how-to-know-my-body-fat-percentage","status":"publish","type":"post","link":"https:\/\/metaboliboost.com\/articles\/how-to-know-my-body-fat-percentage\/","title":{"rendered":"How to Know My Body Fat Percentage: How Wrong Each Method Is"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\"><strong>There is no way to know my body fat percentage exactly, only to estimate it, and every method carries an error range worth seeing before you trust the figure. A scan is the practical reference. A home scale is precise but can sit several points off. The trend from one method beats any single number.<\/strong><\/p>\n\n\n\n<div class=\"msq-audio\" data-article=\"how-to-know-my-body-fat-percentage\" data-minutes=\"13\">\n<style>.msq-audio{margin:1.25em 0 1.75em;padding:16px 18px;background:#EEF3F8;border:1px solid #CBD8E6;border-radius:12px}\n.msq-audio-lead{margin:0 0 8px;font-size:.95em}.msq-audio audio{width:100%;margin:0 0 12px;display:block}\n.msq-toc-title{margin:0 0 6px;font-weight:700}.msq-toc ol{margin:0;padding:0;list-style:none}\n.msq-toc li{display:flex;gap:10px;align-items:center;padding:6px 6px;border-bottom:1px solid #CBD8E6;border-radius:8px}\n.msq-toc li:last-child{border-bottom:0}.msq-toc li.is-active{background:#fff}\n.msq-toc-play{flex:0 0 auto;width:30px;height:30px;border-radius:50%;border:0;background:#1F4E79;color:#fff;font:inherit;font-size:.72em;line-height:30px;padding:0;cursor:pointer}\n.msq-toc-play.is-playing{background:#B4531A}\n.msq-toc-time{flex:0 0 auto;min-width:3.1em;font-variant-numeric:tabular-nums;color:#4A5560;font-size:.9em}\n.msq-toc a{color:#1B1F24;text-decoration:none;line-height:1.35}.msq-toc li.is-active a{font-weight:700;color:#1F4E79}\n.msq-audio-note{margin:10px 0 0;font-size:.82em;color:#4A5560}\nh2.wp-block-heading[id]{scroll-margin-top:24px}\n.msq-hplay{display:inline-block;vertical-align:middle;width:26px;height:26px;margin:0 0 0 10px;border-radius:50%;border:0;background:#1F4E79;cursor:pointer;padding:0;position:relative;top:-2px}\n.msq-hplay::before{content:'\u25b6\ufe0e';display:block;color:#fff;font-size:11px;line-height:26px;text-align:center}\n.msq-hplay.is-playing{background:#B4531A}.msq-hplay.is-playing::before{content:'\u2016';font-size:13px;font-weight:700}\n.msq-bar{position:fixed;left:0;right:0;bottom:0;z-index:9000;display:flex;align-items:center;gap:10px;padding:8px 12px;padding-bottom:calc(8px + env(safe-area-inset-bottom));background:#FFFFFF;border-top:1px solid #CBD8E6;box-shadow:0 -4px 16px rgba(0,0,0,.08);font-size:.92em;color:#1B1F24;transition:transform .2s ease}\n.msq-bar.is-hidden{transform:translateY(130%)}\n.msq-bar-play{display:inline-flex;align-items:center;gap:8px;border:0;border-radius:999px;background:#1F4E79;color:#fff;font:inherit;font-weight:700;padding:8px 14px 8px 12px;cursor:pointer;white-space:nowrap}\n.msq-bar-play.is-playing{background:#B4531A}\n.msq-bar-icon::before{content:'\u25b6\ufe0e';font-size:12px}.msq-bar-play.is-playing .msq-bar-icon::before{content:'\u2016';font-size:14px;font-weight:700}\n.msq-bar-chapter{flex:1 1 auto;min-width:0;overflow:hidden;text-overflow:ellipsis;white-space:nowrap}\n.msq-bar-time{flex:0 0 auto;font-variant-numeric:tabular-nums;color:#4A5560;font-size:.9em}\n.msq-bar-rate,.msq-bar-close{flex:0 0 auto;border:1px solid #CBD8E6;background:#fff;color:#1B1F24;font:inherit;font-size:.85em;line-height:1;border-radius:8px;padding:7px 9px;cursor:pointer}\n.msq-bar-close::before{content:'\u2715'}\n.msq-bar.msq-bar-pill{left:auto;right:14px;bottom:14px;padding:6px;padding-bottom:6px;border:1px solid #CBD8E6;border-radius:999px;box-shadow:0 6px 20px rgba(0,0,0,.15)}\n.msq-bar.msq-bar-pill .msq-bar-chapter,.msq-bar.msq-bar-pill .msq-bar-time,.msq-bar.msq-bar-pill .msq-bar-rate{display:none}\nbody.msq-has-bar{padding-bottom:76px}\n@media (max-width:600px){.msq-bar-time{display:none}.msq-bar{gap:8px;padding-left:10px;padding-right:10px}}\n.msq-s.msq-now{background:#EEF3F8;box-shadow:0 2px 0 #1F4E79;border-radius:2px}\ntr.msq-now td,tr.msq-now th{background:#EEF3F8;box-shadow:inset 0 -2px 0 #1F4E79}\n@media (hover:hover){.msq-s,tr[data-i]{cursor:pointer}.msq-s:hover{background:#EEF3F8}}<\/style>\n<script type=\"application\/ld+json\">{\"@context\":\"https:\/\/schema.org\",\"@type\":\"AudioObject\",\"@id\":\"https:\/\/metaboliboost.com\/articles\/how-to-know-my-body-fat-percentage\/#audio\",\"name\":\"How to Know My Body Fat Percentage: How Wrong Each Method Is, read aloud\",\"description\":\"Synthetic voice reading of the article, recorded 25 September 2026.\",\"contentUrl\":\"https:\/\/metaboliboost.com\/articles\/wp-content\/uploads\/2026\/09\/how-to-know-my-body-fat-percentage-audio-202609251859.mp3\",\"encodingFormat\":\"audio\/mpeg\",\"duration\":\"PT12M34S\",\"uploadDate\":\"2026-09-25\",\"inLanguage\":\"en-US\",\"isAccessibleForFree\":true,\"mainEntityOfPage\":\"https:\/\/metaboliboost.com\/articles\/how-to-know-my-body-fat-percentage\/\",\"hasPart\":[{\"@type\":\"Clip\",\"name\":\"How to Know My Body Fat Percentage: How Wrong Each Method Is\",\"startOffset\":0,\"endOffset\":44},{\"@type\":\"Clip\",\"name\":\"What are the real ways to know my body fat percentage?\",\"startOffset\":44,\"endOffset\":257,\"url\":\"https:\/\/metaboliboost.com\/articles\/how-to-know-my-body-fat-percentage\/#what-are-the-real-ways-to-know-my-body-fat-percentage\"},{\"@type\":\"Clip\",\"name\":\"Why does the number on my bathroom scale move so much?\",\"startOffset\":257,\"endOffset\":355,\"url\":\"https:\/\/metaboliboost.com\/articles\/how-to-know-my-body-fat-percentage\/#why-does-the-number-on-my-bathroom-scale-move-so-much\"},{\"@type\":\"Clip\",\"name\":\"How much does the number have to move before the change is real?\",\"startOffset\":355,\"endOffset\":436,\"url\":\"https:\/\/metaboliboost.com\/articles\/how-to-know-my-body-fat-percentage\/#how-much-does-the-number-have-to-move-before-the-change-is-r\"},{\"@type\":\"Clip\",\"name\":\"What do people who compared a scan with a scale actually report?\",\"startOffset\":436,\"endOffset\":601,\"url\":\"https:\/\/metaboliboost.com\/articles\/how-to-know-my-body-fat-percentage\/#what-do-people-who-compared-a-scan-with-a-scale-actually-rep\"},{\"@type\":\"Clip\",\"name\":\"Is a DXA scan worth paying for?\",\"startOffset\":601,\"endOffset\":669,\"url\":\"https:\/\/metaboliboost.com\/articles\/how-to-know-my-body-fat-percentage\/#is-a-dxa-scan-worth-paying-for\"},{\"@type\":\"Clip\",\"name\":\"What is worth tracking instead?\",\"startOffset\":669,\"endOffset\":754,\"url\":\"https:\/\/metaboliboost.com\/articles\/how-to-know-my-body-fat-percentage\/#what-is-worth-tracking-instead\"}],\"contentSize\":\"5.3 MB\"}<\/script>\n<p class=\"msq-audio-lead\"><strong>Listen to this article<\/strong>, about 13 minutes. A synthetic voice reads the article and announces each section title as it begins; tables are read row by row and the questions at the end are left out.<\/p>\n<audio class=\"msq-audio-player\" controls preload=\"metadata\" src=\"https:\/\/metaboliboost.com\/articles\/wp-content\/uploads\/2026\/09\/how-to-know-my-body-fat-percentage-audio-202609251859.mp3\"><\/audio>\n<nav class=\"msq-toc\" aria-label=\"In this article\"><p class=\"msq-toc-title\">In this article<\/p>\n<ol>\n<li data-start=\"0.0\"><button type=\"button\" class=\"msq-toc-play\" data-start=\"0.0\" aria-label=\"Play from: How to Know My Body Fat Percentage: How Wrong Each Method Is\">&#x25B6;&#xFE0E;<\/button><span class=\"msq-toc-time\">0:00<\/span><a href=\"#top\">How to Know My Body Fat Percentage: How Wrong Each Method Is<\/a><\/li>\n<li data-start=\"44.1\"><button type=\"button\" class=\"msq-toc-play\" data-start=\"44.1\" aria-label=\"Play from: What are the real ways to know my body fat percentage?\">&#x25B6;&#xFE0E;<\/button><span class=\"msq-toc-time\">0:44<\/span><a href=\"#what-are-the-real-ways-to-know-my-body-fat-percentage\">What are the real ways to know my body fat percentage?<\/a><\/li>\n<li data-start=\"256.76\"><button type=\"button\" class=\"msq-toc-play\" data-start=\"256.76\" aria-label=\"Play from: Why does the number on my bathroom scale move so much?\">&#x25B6;&#xFE0E;<\/button><span class=\"msq-toc-time\">4:17<\/span><a href=\"#why-does-the-number-on-my-bathroom-scale-move-so-much\">Why does the number on my bathroom scale move so much?<\/a><\/li>\n<li data-start=\"354.74\"><button type=\"button\" class=\"msq-toc-play\" data-start=\"354.74\" aria-label=\"Play from: How much does the number have to move before the change is real?\">&#x25B6;&#xFE0E;<\/button><span class=\"msq-toc-time\">5:55<\/span><a href=\"#how-much-does-the-number-have-to-move-before-the-change-is-r\">How much does the number have to move before the change is real?<\/a><\/li>\n<li data-start=\"436.2\"><button type=\"button\" class=\"msq-toc-play\" data-start=\"436.2\" aria-label=\"Play from: What do people who compared a scan with a scale actually report?\">&#x25B6;&#xFE0E;<\/button><span class=\"msq-toc-time\">7:16<\/span><a href=\"#what-do-people-who-compared-a-scan-with-a-scale-actually-rep\">What do people who compared a scan with a scale actually report?<\/a><\/li>\n<li data-start=\"600.58\"><button type=\"button\" class=\"msq-toc-play\" data-start=\"600.58\" aria-label=\"Play from: Is a DXA scan worth paying for?\">&#x25B6;&#xFE0E;<\/button><span class=\"msq-toc-time\">10:01<\/span><a href=\"#is-a-dxa-scan-worth-paying-for\">Is a DXA scan worth paying for?<\/a><\/li>\n<li data-start=\"668.88\"><button type=\"button\" class=\"msq-toc-play\" data-start=\"668.88\" aria-label=\"Play from: What is worth tracking instead?\">&#x25B6;&#xFE0E;<\/button><span class=\"msq-toc-time\">11:09<\/span><a href=\"#what-is-worth-tracking-instead\">What is worth tracking instead?<\/a><\/li>\n<\/ol><\/nav>\n<p class=\"msq-audio-note\">Recorded 25 September 2026 from the article as published that day. Press a chapter to jump there; the highlighted line is what is playing. A play button sits beside every section heading, and once you scroll past this player a bar at the bottom of the screen keeps the controls in reach. Tap or click any sentence to hear the reading start from there.<\/p>\n<script>var MSQ_SENT = [[0.0,\"h\",\"howtoknowmybodyfatpercen\",48],[3.76,\"p\",\"thereisnowaytoknowmybody\",127],[13.8,\"p\",\"ascanisthepracticalrefer\",28],[16.72,\"p\",\"ahomescaleisprecisebutca\",44],[20.72,\"p\",\"thetrendfromonemethodbea\",41],[24.56,\"p\",\"onthispageeverymethodwit\",240],[44.1,\"h\",\"whataretherealwaystoknow\",43],[47.46,\"p\",\"themethodsapersoncanactu\",164],[58.26,\"p\",\"mostarticleslistthem\",20],[59.9,\"p\",\"almostnonesayhowfareacho\",88],[66.54,\"p\",\"hereisthatcolumncompiled\",102],[73.18,\"t\",\"estimatefrombmi\",248],[94.38,\"t\",\"consumerimpedancescalefo\",292],[120.9,\"t\",\"multifrequencyimpedanceh\",293],[146.5,\"t\",\"skinfoldcalipers\",285],[169.26,\"t\",\"tapemeasurecircumference\",211],[187.3,\"t\",\"airdisplacementthepod\",257],[208.38,\"t\",\"dxascan\",296],[233.34,\"p\",\"twothingsfalloutofthatta\",27],[234.9,\"p\",\"theestimatefrombmiisnota\",181],[247.46,\"p\",\"andeventhereferencemetho\",34],[249.82,\"p\",\"nobodyhereishandingoutth\",86],[256.76,\"h\",\"whydoesthenumberonmybath\",43],[260.12,\"p\",\"aconsumerimpedancescaleh\",46],[264.0,\"p\",\"itweighsyouanditsendsasm\",76],[269.96,\"p\",\"fatmassmusclemassbonemas\",133],[278.52,\"p\",\"ifyouarenotmuchlikethatr\",63],[282.44,\"p\",\"resistancedependsonwater\",128],[291.24,\"p\",\"thatpartiswellknown\",19],[292.36,\"p\",\"theoddresultthatturnsupw\",67],[297.24,\"p\",\"abritishjournalofnutriti\",142],[307.36,\"p\",\"therepeatabilitywasexcel\",72],[314.64,\"p\",\"theaccuracywasnot\",17],[315.8,\"p\",\"constanterroragainstther\",85],[323.08,\"p\",\"preciseandcorrectarenott\",75],[328.2,\"p\",\"thedetailworthstealingfr\",129],[338.48,\"p\",\"theyflaggeditassuspiciou\",100],[344.88,\"p\",\"ascalethatneverdisagrees\",51],[348.72,\"p\",\"itisbeingquiet\",14],[349.96,\"p\",\"andadevicethatwillnotmov\",51],[354.74,\"h\",\"howmuchdoesthenumberhave\",51],[357.62,\"p\",\"thisisthequestionnobodya\",54],[361.22,\"p\",\"bonedensityclinicsuselea\",90],[367.78,\"p\",\"belowthatachangeismeasur\",55],[372.58,\"p\",\"aboveitsomethingrealprob\",36],[375.5,\"p\",\"thesamearithmeticworkson\",75],[380.7,\"p\",\"runitonthenumbersabove\",22],[382.06,\"p\",\"ascalewithaprecisionerro\",82],[392.78,\"p\",\"soareadingthatdriftsfrom\",49],[397.62,\"p\",\"adriftto296isprobablyrea\",25],[400.94,\"p\",\"runitonthedxafiguresandt\",236],[422.58,\"p\",\"thecatchiswhythiscalcula\",46],[425.74,\"p\",\"noconsumerscalemanufactu\",104],[432.98,\"p\",\"independentstudiesarethe\",41],[436.2,\"h\",\"whatdopeoplewhocompareda\",52],[440.28,\"p\",\"ireadthereviewpagesforfo\",158],[451.48,\"p\",\"sixwerespecificenoughtou\",26],[453.44,\"p\",\"theseareaccountsnotevide\",120],[461.08,\"p\",\"ontrustpilotareviewerpos\",180],[477.28,\"p\",\"onthesamepageareviewerpo\",139],[491.76,\"p\",\"onanotherbrandpagearevie\",132],[503.92,\"p\",\"inanrloseitthreadfromjun\",241],[522.48,\"p\",\"thatisastrangerontheinte\",151],[532.28,\"p\",\"inthesamethreadacommente\",145],[542.52,\"p\",\"theaccountsthatcuttheoth\",41],[544.72,\"p\",\"inaseptember2025threadap\",222],[560.24,\"p\",\"theirscalewasbadlywrongo\",76],[565.76,\"p\",\"inthesamethreadacommente\",196],[581.4,\"p\",\"thesixtogethersitwiththe\",52],[584.84,\"p\",\"theyagreeondirectionthes\",43],[587.6,\"p\",\"theydisagreeonhowroughon\",115],[595.92,\"p\",\"nobodyintheseaccountscou\",63],[600.58,\"h\",\"isadxascanworthpayingfor\",24],[603.42,\"p\",\"itdependswhatyouwantfrom\",26],[604.74,\"p\",\"asaoneoffpictureofwheref\",85],[612.46,\"p\",\"thebritishheartfoundatio\",159],[626.18,\"p\",\"affordableonceexpensivea\",31],[628.58,\"p\",\"asawayoftrackingchangeas\",54],[633.34,\"p\",\"machinesfromdifferentman\",153],[643.66,\"p\",\"compareoneclinicwithanot\",69],[648.14,\"p\",\"samemachineornocompariso\",25],[650.22,\"p\",\"onethingtoholdseparately\",46],[652.74,\"p\",\"ifwatchingthisnumberisca\",143],[662.14,\"p\",\"measurementaccuracyisnot\",83],[668.88,\"h\",\"whatisworthtrackinginste\",26],[670.72,\"p\",\"notthatmeasurementishope\",28],[672.2,\"p\",\"atrendfromoneconsistentm\",75],[677.24,\"p\",\"pickonetooluseitunderthe\",79],[684.32,\"p\",\"alongsideittrackwhatcanb\",37],[686.44,\"p\",\"weightisonetheonlyfigure\",84],[693.44,\"p\",\"waisttoheightrationeedso\",135],[702.48,\"p\",\"itisonlyasgoodastheplace\",149],[712.0,\"p\",\"strengthinthegymandhowcl\",111],[718.6,\"p\",\"ournoteonweightlossversu\",76],[724.32,\"p\",\"twootherpiecesherearewor\",46],[726.8,\"p\",\"differencesinhowmenandwo\",133],[735.56,\"p\",\"andifyourfigurehasstoppe\",139],[744.12,\"p\",\"thisarticleisgeneralinfo\",109],[750.8,\"p\",\"speaktoyourdoctoraboutyo\",38]];\n(function(){\n  function init(){\n  var root = document.querySelector('.msq-audio'); if (!root) { return; }\n  var audio = root.querySelector('audio'), items = Array.prototype.slice.call(root.querySelectorAll('.msq-toc li'));\n  var starts = items.map(function(li){ return parseFloat(li.getAttribute('data-start')) || 0; });\n  var names = items.map(function(li){ return li.querySelector('a').textContent; });\n  var anchors = items.map(function(li){ var h = li.querySelector('a').getAttribute('href') || ''; return (h.charAt(0) === '#' && h !== '#top') ? document.getElementById(h.slice(1)) : null; });\n  var article = root.getAttribute('data-article') || location.pathname, minutes = root.getAttribute('data-minutes') || '';\n  var marks = {}, started = false, pausedAt = -1, closed = false, ended = false;\n  var RATES = [1, 1.25, 1.5], rate = 1;\n  try { var saved = parseFloat(localStorage.getItem('msq-audio-rate')); if (RATES.indexOf(saved) >= 0) { rate = saved; } } catch (e) {}\n  audio.playbackRate = rate;\n  function track(name, extra){ try { if (typeof gtag === 'function') { var p = { article: article }; for (var k in extra) { p[k] = extra[k]; } gtag('event', name, p); } } catch (e) {} }\n  function current(){ var t = audio.currentTime, idx = 0; for (var i = 0; starts.length > i; i += 1) { if (t + 0.25 >= starts[i]) { idx = i; } } return idx; }\n  function onScreen(){\n    var line = window.innerHeight \/ 3, idx = 0;\n    for (var i = 0; anchors.length > i; i += 1) { var el = anchors[i]; if (el && line >= el.getBoundingClientRect().top) { idx = i; } }\n    return idx;\n  }\n  function fmt(s){ s = Math.max(0, Math.round(s || 0)); var m = Math.floor(s \/ 60), r = s % 60; return m + ':' + (10 > r ? '0' : '') + r; }\n  function play(from, source){\n    if (from !== null) { audio.currentTime = from; }\n    var p = audio.play(); if (p && p.catch) { p.catch(function(){}); }\n    track(from === null ? 'audio_resume' : 'audio_chapter', { chapter: names[current()], start: Math.round(audio.currentTime), source: source });\n  }\n  var hbtns = anchors.map(function(el, i){\n    if (!el) { return null; }\n    var b = document.createElement('button'); b.type = 'button'; b.className = 'msq-hplay'; b.setAttribute('aria-label', 'Play this section: ' + names[i]);\n    b.addEventListener('click', function(){\n      if (!audio.paused && current() === i) { audio.pause(); track('audio_pause', { source: 'heading' }); return; }\n      play(starts[i], 'heading');\n    });\n    el.appendChild(b); return b;\n  });\n  var bar = document.createElement('div'); bar.className = 'msq-bar msq-bar-pill is-hidden'; bar.setAttribute('role', 'region'); bar.setAttribute('aria-label', 'Audio player');\n  var playBtn = document.createElement('button'); playBtn.type = 'button'; playBtn.className = 'msq-bar-play';\n  var icon = document.createElement('span'); icon.className = 'msq-bar-icon'; icon.setAttribute('aria-hidden', 'true');\n  var label = document.createElement('span'); label.className = 'msq-bar-label';\n  playBtn.appendChild(icon); playBtn.appendChild(label);\n  var chap = document.createElement('span'); chap.className = 'msq-bar-chapter';\n  var clock = document.createElement('span'); clock.className = 'msq-bar-time';\n  var rateBtn = document.createElement('button'); rateBtn.type = 'button'; rateBtn.className = 'msq-bar-rate'; rateBtn.setAttribute('aria-label', 'Playback speed');\n  var closeBtn = document.createElement('button'); closeBtn.type = 'button'; closeBtn.className = 'msq-bar-close'; closeBtn.setAttribute('aria-label', 'Close the audio bar');\n  bar.appendChild(playBtn); bar.appendChild(chap); bar.appendChild(clock); bar.appendChild(rateBtn); bar.appendChild(closeBtn);\n  document.body.appendChild(bar);\n  function showRate(){ rateBtn.textContent = (rate === 1 ? '1' : String(rate)) + 'x'; }\n  showRate();\n  rateBtn.addEventListener('click', function(){\n    rate = RATES[(RATES.indexOf(rate) + 1) % RATES.length]; audio.playbackRate = rate; showRate();\n    try { localStorage.setItem('msq-audio-rate', String(rate)); } catch (e) {}\n    track('audio_rate', { rate: rate });\n  });\n  closeBtn.addEventListener('click', function(){\n    closed = true; if (!audio.paused) { audio.pause(); } paint(); track('audio_bar_close', {});\n  });\n  function mode(){\n    if (!audio.paused) { return 'pause'; }\n    if (ended) { return 'again'; }\n    if (!started) { return 'listen'; }\n    return (pausedAt === onScreen()) ? 'resume' : 'section';\n  }\n  playBtn.addEventListener('click', function(){\n    var m = mode();\n    if (m === 'pause') { audio.pause(); track('audio_pause', { source: 'bar' }); return; }\n    if (m === 'again') { ended = false; play(0, 'bar'); return; }\n    if (m === 'resume') { play(null, 'bar'); return; }\n    play(starts[onScreen()], 'bar');\n  });\n  function paint(){\n    var idx = current(), playing = !audio.paused, m = mode();\n    items.forEach(function(li, i){\n      var on = (i === idx) && playing, b = li.querySelector('.msq-toc-play'), a = li.querySelector('a');\n      li.classList.toggle('is-active', on); b.classList.toggle('is-playing', on);\n      b.textContent = on ? '\u2016' : '\u25b6\ufe0e';\n      b.setAttribute('aria-label', (on ? 'Pause: ' : 'Play from: ') + a.textContent);\n    });\n    hbtns.forEach(function(b, i){ if (b) { var on = (i === idx) && playing; b.classList.toggle('is-playing', on); b.setAttribute('aria-label', (on ? 'Pause this section: ' : 'Play this section: ') + names[i]); } });\n    playBtn.classList.toggle('is-playing', playing);\n    label.textContent = m === 'pause' ? 'Pause' : m === 'again' ? 'Play again' : m === 'resume' ? 'Resume' : m === 'section' ? 'Play this section' : 'Listen, ' + minutes + ' min';\n    playBtn.setAttribute('aria-label', label.textContent);\n    chap.textContent = started ? names[(playing || m === 'resume') ? idx : onScreen()] : '';\n    clock.textContent = started ? fmt(audio.currentTime) + ' \/ ' + fmt(audio.duration) : '';\n    bar.classList.toggle('msq-bar-pill', !started);\n    var show = !closed && (started || 0 > root.getBoundingClientRect().bottom);\n    bar.classList.toggle('is-hidden', !show);\n    document.body.classList.toggle('msq-has-bar', show);\n  }\n  root.addEventListener('click', function(e){\n    var b = e.target.closest ? e.target.closest('.msq-toc-play') : null; if (!b) { return; }\n    var li = b.parentNode, s = parseFloat(b.getAttribute('data-start')) || 0;\n    if (!audio.paused && current() === items.indexOf(li)) { audio.pause(); track('audio_pause', { source: 'index' }); return; }\n    play(s, 'index');\n  });\n  audio.addEventListener('play', function(){ ended = false; closed = false; if (!started) { started = true; track('audio_play', { minutes: Math.round((audio.duration || 0) \/ 60) }); } paint(); });\n  audio.addEventListener('pause', function(){ pausedAt = current(); paint(); });\n  audio.addEventListener('timeupdate', function(){\n    paint();\n    if (audio.duration > 0) {\n      var pct = Math.floor(audio.currentTime \/ audio.duration * 100);\n      [25, 50, 75].forEach(function(m){ if (pct >= m && !marks[m]) { marks[m] = true; track('audio_progress', { percent: m }); } });\n    }\n  });\n  audio.addEventListener('ended', function(){ ended = true; track('audio_complete', {}); paint(); });\n  var ticking = false;\n  function onScroll(){ if (ticking) { return; } ticking = true; setTimeout(function(){ ticking = false; paint(); }, 80); }\n  window.addEventListener('scroll', onScroll, { passive: true }); window.addEventListener('resize', onScroll);\n  paint();\n  }\n  if (document.readyState === 'loading') { document.addEventListener('DOMContentLoaded', init); } else { init(); }\n})();\n\n(function(){\n  function start(){\n    var root = document.querySelector('.msq-audio'), audio = root ? root.querySelector('audio') : null;\n    var map = (typeof MSQ_SENT !== 'undefined') ? MSQ_SENT : [];\n    if (!root || !audio || !map.length) { return; }\n    var scope = root.closest('main') || root.closest('article') || root.closest('.entry-content') || document.body;\n    var SKIP = '.msq-audio,.msq,.msq-tool,.msq-end,.msq-bar,script,style,noscript,figcaption,#rank-math-faq,.rank-math-block,nav,header,footer';\n    function norm(s){ return s.toLowerCase().replace(\/[^a-z0-9]+\/g, ''); }\n    var nodes = [], stream = '', walker = document.createTreeWalker(scope, NodeFilter.SHOW_TEXT, null), n;\n    while ((n = walker.nextNode())) {\n      var el = n.parentElement; if (!el || el.closest(SKIP)) { continue; }\n      var raw = n.nodeValue, keep = [], norms = '';\n      for (var i = 0; raw.length > i; i += 1) { var c = raw.charAt(i).toLowerCase(); if (\/[a-z0-9]\/.test(c)) { keep.push(i); norms += c; } }\n      if (!norms) { continue; }\n      nodes.push({ node: n, a: stream.length, b: stream.length + norms.length, keep: keep });\n      stream += norms;\n    }\n    var segs = [], cursor = 0, lastRow = null;\n    map.forEach(function(m, idx){\n      var kind = m[1], f = m[2], len = m[3];\n      if (kind === 't') {\n        var rows = scope.querySelectorAll('tr'), after = !lastRow;\n        for (var r = 0; rows.length > r; r += 1) {\n          var tr = rows[r];\n          if (!after) { if (tr === lastRow) { after = true; } continue; }\n          var cell = tr.querySelector('td,th');\n          if (cell && norm(cell.textContent).indexOf(f) === 0) { tr.setAttribute('data-i', idx); lastRow = tr; break; }\n        }\n        return;\n      }\n      var p = stream.indexOf(f, cursor); if (0 > p) { return; }\n      segs.push({ i: idx, a: p, b: Math.min(p + len, stream.length) }); cursor = p + len;\n    });\n    var si = 0;\n    nodes.forEach(function(nd){\n      var frag = document.createDocumentFragment(), raw = nd.node.nodeValue, rawPos = 0, any = false;\n      for (var k = si; segs.length > k; k += 1) {\n        var sg = segs[k]; if (sg.a >= nd.b) { break; } if (nd.a >= sg.b) { continue; }\n        var s = Math.max(sg.a, nd.a), e = Math.min(sg.b, nd.b);\n        var rs = nd.keep[s - nd.a], re2 = nd.keep[e - nd.a - 1] + 1;\n        if (rs > rawPos) { frag.appendChild(document.createTextNode(raw.slice(rawPos, rs))); }\n        var span = document.createElement('span'); span.className = 'msq-s'; span.setAttribute('data-i', sg.i); span.textContent = raw.slice(rs, re2);\n        frag.appendChild(span); rawPos = re2; any = true;\n        if (sg.b > nd.b) { break; }\n      }\n      while (segs.length > si && nd.b >= segs[si].b) { si += 1; }\n      if (!any) { return; }\n      if (raw.length > rawPos) { frag.appendChild(document.createTextNode(raw.slice(rawPos))); }\n      nd.node.parentNode.replaceChild(frag, nd.node);\n    });\n    var starts = map.map(function(m){ return m[0]; }), curIdx = -1, lastUser = 0, timer = null, autoUntil = 0, dragging = false;\n    function idxAt(t){ var lo = 0, hi = starts.length; while (hi > lo + 1) { var mid = (lo + hi) >> 1; if (t + 0.15 >= starts[mid]) { lo = mid; } else { hi = mid; } } return (t + 0.15 >= starts[0]) ? lo : -1; }\n    function setNow(i){\n      if (i === curIdx) { return; }\n      Array.prototype.forEach.call(scope.querySelectorAll('.msq-now'), function(el){ el.classList.remove('msq-now'); });\n      curIdx = i; if (0 > i) { return; }\n      var els = scope.querySelectorAll('[data-i=\"' + i + '\"]'); if (!els.length) { return; }\n      Array.prototype.forEach.call(els, function(el){ el.classList.add('msq-now'); });\n      var r = els[0].getBoundingClientRect(), now = Date.now();\n      if (!dragging && now > lastUser + 2500 && (80 > r.top || r.bottom > window.innerHeight - 140)) {\n        var reduce = window.matchMedia && window.matchMedia('(prefers-reduced-motion: reduce)').matches;\n        autoUntil = now + (reduce ? 400 : 1600);\n        els[0].scrollIntoView({ block: 'center', behavior: reduce ? 'auto' : 'smooth' });\n      }\n    }\n    function tick(){ if (!audio.paused) { setNow(idxAt(audio.currentTime)); } }\n    function userScrolled(){ lastUser = Date.now(); }\n    ['wheel', 'touchmove', 'keydown'].forEach(function(ev){ window.addEventListener(ev, userScrolled, { passive: true }); });\n    window.addEventListener('scroll', function(){ if (Date.now() > autoUntil) { userScrolled(); } }, { passive: true });\n    window.addEventListener('mousedown', function(e){ if (e.clientX >= document.documentElement.clientWidth) { dragging = true; userScrolled(); } }, { passive: true });\n    window.addEventListener('mouseup', function(){ if (dragging) { dragging = false; userScrolled(); } }, { passive: true });\n    audio.addEventListener('play', function(){ if (timer) { clearInterval(timer); } timer = setInterval(tick, 150); tick(); });\n    audio.addEventListener('pause', function(){ if (timer) { clearInterval(timer); timer = null; } });\n    scope.addEventListener('click', function(e){\n      if (e.target.closest('a, button, input, select, textarea, label, summary, .msq, .msq-tool, .msq-end, .msq-audio, .msq-bar')) { return; }\n      var sel = window.getSelection ? String(window.getSelection()) : '';\n      if (sel && sel.trim()) { return; }\n      var el = e.target.closest('[data-i]'); if (!el) { return; }\n      var i = parseInt(el.getAttribute('data-i'), 10); if (isNaN(i)) { return; }\n      if (!audio.paused && i === curIdx) { return; }\n      lastUser = Date.now();\n      audio.currentTime = starts[i];\n      var p = audio.play(); if (p && p.catch) { p.catch(function(){}); }\n      try { if (typeof gtag === 'function') { gtag('event', 'audio_chapter', { article: location.pathname, source: 'sentence', start: Math.round(starts[i]) }); } } catch (err) {}\n    });\n    audio.addEventListener('seeked', tick);\n    audio.addEventListener('ended', function(){ setNow(-1); });\n  }\n  if (document.readyState === 'loading') { document.addEventListener('DOMContentLoaded', start); } else { start(); }\n})();<\/script>\n<\/div>\n\n\n\n<p class=\"msq-hook wp-block-paragraph\">On this page: every method with the one column the others leave out, how far each can sit from the reference, why a bathroom scale can be precise and wrong at once, the formula that says when a change is real, what six people who compared a scan with a scale reported, and what is worth tracking instead.<\/p>\n\n\n\n<div class=\"msq\" id=\"ms-quiz\" data-slug=\"how-to-know-my-body-fat-percentage\" data-category=\"metabolism and weight\" data-list=\"1\">\n<style>.msq,.msq-hook,.msq-box,.msq-end,.msq-tool{--msq-accent:#1F4E79;--msq-accent-text:#FFFFFF;--msq-line:#CBD8E6;--msq-warn:#B4531A;--msq-muted:#4A5560;--msq-tint:#EEF3F8;--msq-base:#FFFFFF}\n.msq{margin:1.25em 0 1.75em}\n.msq-hook{border-left:3px solid var(--msq-accent);padding:6px 14px;color:var(--msq-muted);font-size:.97em}\n.msq-box{background:var(--msq-tint);border:1px solid var(--msq-line);border-radius:12px;padding:0}\n.msq-box>summary{cursor:pointer;list-style:none;padding:14px 18px;font-weight:700;color:var(--msq-accent)}\n.msq-box>summary::-webkit-details-marker{display:none}\n.msq-box>summary::before{content:\"+\";display:inline-block;width:1.1em;font-weight:800}\n.msq-box[open]>summary::before{content:\"\\00d7\"}\n.msq-body{padding:2px 18px 18px}\n.msq-intro{margin:0 0 12px;font-size:.95em;color:var(--msq-muted)}\n.msq-list{margin:0;padding:0;list-style:none}\n.msq-q{margin:0 0 18px;padding:0}\n.msq-question{font-weight:700;margin:0 0 8px}\n.msq-options{display:flex;flex-direction:column;gap:8px}\n.msq-opt{text-align:left;background:var(--msq-base);border:1px solid var(--msq-line);border-radius:8px;padding:10px 12px;font:inherit;font-size:.95em;color:inherit;cursor:pointer;line-height:1.35}\n.msq-opt:hover{border-color:var(--msq-accent)}\n.msq-opt[disabled]{cursor:default}\n.msq-opt.is-right{border-color:var(--msq-accent);background:var(--msq-line);font-weight:700}\n.msq-opt.is-wrong{border-color:var(--msq-warn);color:var(--msq-warn)}\n.msq-explain{margin:8px 0 0;font-size:.92em;padding:10px 12px;border-left:3px solid var(--msq-accent);background:var(--msq-base);border-radius:0 8px 8px 0}\n.msq-explain[hidden]{display:none}\n.msq-verdict{font-weight:700}\n.msq-result{margin-top:14px;padding:14px 16px;background:var(--msq-base);border:1px solid var(--msq-line);border-radius:10px}\n.msq-result[hidden]{display:none}\n.msq-result h3{margin:0 0 6px;font-size:1.1em}\n.msq-result p{margin:0 0 8px}\n.msq-jump{margin:0 0 8px;padding-left:1.2em}\n.msq-form{margin-top:10px;display:flex;flex-wrap:wrap;gap:8px;align-items:center}\n.msq-form input[type=email]{flex:1 1 220px;padding:10px 12px;border:1px solid var(--msq-muted);border-radius:8px;font:inherit;background:#fff}\n.msq-btn{background:var(--msq-accent);color:var(--msq-accent-text);border:0;border-radius:8px;padding:11px 18px;font:inherit;font-weight:700;cursor:pointer}\n.msq-btn:hover{filter:brightness(.92)}\n.msq-btn[disabled]{opacity:.7;cursor:default}\n.msq-no{font-size:.9em;color:var(--msq-muted);margin-left:4px}\n.msq-privacy{margin:6px 0 0;font-size:.82em;color:var(--msq-muted);flex-basis:100%}\n.msq-hp{position:absolute;left:-5000px;width:1px;height:1px;overflow:hidden}\n.msq-msg{margin:8px 0 0;font-size:.92em}\n.msq-end{margin:1.5em 0;padding:18px;border:1px solid var(--msq-accent);border-radius:12px;text-align:center;background:var(--msq-tint)}\n.msq-end p{margin:0 0 12px}\n.msq-end .msq-body{text-align:left;padding:16px 0 0}\n.msq-end .msq-start-test[hidden]{display:none}\n.msq-tool{margin:1.5em 0;padding:18px 20px;background:var(--msq-tint);border:1px solid var(--msq-line);border-radius:12px}\n.msq-tool h3{margin:0 0 6px;font-size:1.15em}\n.msq-tool p{margin:0 0 10px}\n.msq-tool .msq-note{font-size:.85em;color:var(--msq-muted);margin:10px 0 0}\n.msq-check label{display:flex;gap:10px;align-items:flex-start;padding:9px 0;border-bottom:1px solid var(--msq-line);cursor:pointer;line-height:1.4}\n.msq-check label:last-of-type{border-bottom:0}\n.msq-check input{margin-top:5px;flex:0 0 auto;width:18px;height:18px;accent-color:var(--msq-accent)}\n.msq-check-count{font-weight:700;margin:10px 0 0}\n.msq-verdict-box{margin:12px 0 0;padding:10px 14px;border-radius:8px;background:var(--msq-base);border-left:3px solid var(--msq-warn)}\n.msq-verdict-box[hidden]{display:none}\n.msq-calc{display:grid;grid-template-columns:1fr 1fr;gap:10px 16px}\n.msq-calc label{display:flex;flex-direction:column;gap:4px;font-size:.92em}\n.msq-calc input,.msq-calc select{padding:8px 10px;border:1px solid var(--msq-muted);border-radius:8px;font:inherit;background:#fff}\n.msq-calc-out{grid-column:1 \/ -1;margin-top:6px;padding:12px 14px;background:var(--msq-base);border-radius:8px;border:1px solid var(--msq-line)}\n.msq-calc-out strong{font-size:1.15em}\n.msq-choose label{display:block;padding:9px 12px;margin:0 0 8px;background:var(--msq-base);border:1px solid var(--msq-line);border-radius:8px;cursor:pointer}\n.msq-choose input{margin-right:8px;accent-color:var(--msq-accent)}\n.msq-choice-result{margin-top:10px;padding:12px 14px;background:var(--msq-base);border-left:3px solid var(--msq-accent);border-radius:0 8px 8px 0}\n.msq-choice-result[hidden]{display:none}\n@media (max-width:600px){.msq-calc{grid-template-columns:1fr}}\nh2.wp-block-heading[id]{scroll-margin-top:24px}<\/style>\n<noscript><style>.msq-explain{display:block !important}<\/style><\/noscript>\n<details class=\"msq-box\">\n<summary>Think you already know this? Five questions, one minute.<\/summary>\n<div class=\"msq-body\">\n<p class=\"msq-intro\">Every answer is on this page. Answer from what you know now; the page fills in the rest.<\/p>\n<ol class=\"msq-list\">\n<li class=\"msq-q\" data-q=\"1\" data-answer=\"b\" data-title=\"What are the real ways to know my body fat percentage?\" data-section=\"#what-are-the-real-ways-to-know-my-body-fat-percentage\">\n<p class=\"msq-question\">1. What does an estimate from BMI actually measure?<\/p>\n<div class=\"msq-options\" role=\"group\" aria-label=\"Question 1 options\"><button type=\"button\" class=\"msq-opt\" data-opt=\"a\">Fat directly<\/button><button type=\"button\" class=\"msq-opt\" data-opt=\"b\">Nothing; it is height and weight put through an equation, with a standard error of about four percentage points<\/button><button type=\"button\" class=\"msq-opt\" data-opt=\"c\">Muscle mass<\/button><\/div>\n<p class=\"msq-explain\" hidden><span class=\"msq-verdict\"><\/span><a href=\"https:\/\/www.cdc.gov\/bmi\/adult-calculator\/index.html\" target=\"_blank\" rel=\"noopener\">The CDC<\/a> describes BMI as a calculated measure of weight relative to height. Even the DXA reference has a range: repeat scans varied by 0.7 to 2.6 percent and two manufacturers read about 1.4 points apart on the same person. <a class=\"msq-section\" href=\"#what-are-the-real-ways-to-know-my-body-fat-percentage\">Read the section<\/a><\/p>\n<\/li>\n<li class=\"msq-q\" data-q=\"2\" data-answer=\"b\" data-title=\"Why does the number on my bathroom scale move so much?\" data-section=\"#why-does-the-number-on-my-bathroom-scale-move-so-much\">\n<p class=\"msq-question\">2. In the fifteen device study, what was odd about the five scales that reported almost perfect precision?<\/p>\n<div class=\"msq-options\" role=\"group\" aria-label=\"Question 2 options\"><button type=\"button\" class=\"msq-opt\" data-opt=\"a\">They were the most accurate<\/button><button type=\"button\" class=\"msq-opt\" data-opt=\"b\">The authors suspected the algorithm was restricting how much the output could vary, so a device that never disagrees with itself cannot show a change either<\/button><button type=\"button\" class=\"msq-opt\" data-opt=\"c\">They were broken<\/button><\/div>\n<p class=\"msq-explain\" hidden><span class=\"msq-verdict\"><\/span><a href=\"https:\/\/www.cambridge.org\/core\/journals\/british-journal-of-nutrition\/article\/assessing-the-reliability-and-crosssectional-and-longitudinal-validity-of-fifteen-bioelectrical-impedance-analysis-devices\/EC129A8C9BE88D77DE09A7B8DF400936\" target=\"_blank\" rel=\"noopener\">The British Journal of Nutrition study<\/a> put 73 adults through fifteen devices: precision error ran from 0.0 to 0.49 points while constant error against a four compartment reference ran from 3.5 points low to 11.7 points high. Precise and correct are not the same property. <a class=\"msq-section\" href=\"#why-does-the-number-on-my-bathroom-scale-move-so-much\">Read the section<\/a><\/p>\n<\/li>\n<li class=\"msq-q\" data-q=\"3\" data-answer=\"a\" data-title=\"How much does the number have to move before the change is real?\" data-section=\"#how-much-does-the-number-have-to-move-before-the-change-is-r\">\n<p class=\"msq-question\">3. What is the least significant change for a scale with a precision error of 0.49 percentage points?<\/p>\n<div class=\"msq-options\" role=\"group\" aria-label=\"Question 3 options\"><button type=\"button\" class=\"msq-opt\" data-opt=\"a\">About 1.4 points<\/button><button type=\"button\" class=\"msq-opt\" data-opt=\"b\">About 0.1 points<\/button><button type=\"button\" class=\"msq-opt\" data-opt=\"c\">About 10 points<\/button><\/div>\n<p class=\"msq-explain\" hidden><span class=\"msq-verdict\"><\/span><a href=\"https:\/\/pubmed.ncbi.nlm.nih.gov\/17616413\/\" target=\"_blank\" rel=\"noopener\">The formula bone density clinics use<\/a> is 2.77 times the precision error. A drift from 28.0 to 28.9 has told you nothing; a drift to 29.6 is probably real. The catch is that no consumer manufacturer publishes a precision error, so the one number the sum needs is the one nobody prints on the box. <a class=\"msq-section\" href=\"#how-much-does-the-number-have-to-move-before-the-change-is-r\">Read the section<\/a><\/p>\n<\/li>\n<li class=\"msq-q\" data-q=\"4\" data-answer=\"a\" data-title=\"Is a DXA scan worth paying for?\" data-section=\"#is-a-dxa-scan-worth-paying-for\">\n<p class=\"msq-question\">4. What is the one rule this page gives for tracking change with scans?<\/p>\n<div class=\"msq-options\" role=\"group\" aria-label=\"Question 4 options\"><button type=\"button\" class=\"msq-opt\" data-opt=\"a\">Same machine, or no comparison, because different manufacturers read about 1.4 points apart on the same person<\/button><button type=\"button\" class=\"msq-opt\" data-opt=\"b\">Alternate clinics for a fair average<\/button><button type=\"button\" class=\"msq-opt\" data-opt=\"c\">Scan weekly<\/button><\/div>\n<p class=\"msq-explain\" hidden><span class=\"msq-verdict\"><\/span><a href=\"https:\/\/pubmed.ncbi.nlm.nih.gov\/41986464\/\" target=\"_blank\" rel=\"noopener\">The device conversion study<\/a> is behind that rule, and <a href=\"https:\/\/www.bhf.org.uk\/informationsupport\/heart-matters-magazine\/nutrition\/weight\/best-way-to-measure-body-fat\" target=\"_blank\" rel=\"noopener\">the British Heart Foundation<\/a> puts a UK DEXA scan at least 100 pounds and an air displacement pod from about 40. Affordable once, expensive as a habit. <a class=\"msq-section\" href=\"#is-a-dxa-scan-worth-paying-for\">Read the section<\/a><\/p>\n<\/li>\n<li class=\"msq-q\" data-q=\"5\" data-answer=\"b\" data-title=\"What is worth tracking instead?\" data-section=\"#what-is-worth-tracking-instead\">\n<p class=\"msq-question\">5. Which figure does a home scale measure directly rather than model?<\/p>\n<div class=\"msq-options\" role=\"group\" aria-label=\"Question 5 options\"><button type=\"button\" class=\"msq-opt\" data-opt=\"a\">Body fat percentage<\/button><button type=\"button\" class=\"msq-opt\" data-opt=\"b\">Weight, accurate to grams<\/button><button type=\"button\" class=\"msq-opt\" data-opt=\"c\">Visceral fat<\/button><\/div>\n<p class=\"msq-explain\" hidden><span class=\"msq-verdict\"><\/span>Waist to height ratio needs only a tape and speaks to where fat sits; strength and how clothes fit do not drift with hydration. Pick one tool, use it under the same conditions every time, and read it over weeks rather than days. <a class=\"msq-section\" href=\"#what-is-worth-tracking-instead\">Read the section<\/a><\/p>\n<\/li>\n<\/ol>\n<div class=\"msq-result\" hidden><\/div>\n<\/div>\n<\/details>\n<script>(function(){\n  if (window.__msqInit) { return; }\n  window.__msqInit = true;\n  var root = document.getElementById('ms-quiz');\n  if (!root) { return; }\n  var meta = { slug: root.getAttribute('data-slug'), category: root.getAttribute('data-category'),\n               list: root.getAttribute('data-list') || '1' };\n  function qs(el, s){ return el.querySelector(s); }\n  function qsa(el, s){ return Array.prototype.slice.call(el.querySelectorAll(s)); }\n  function track(name, params){\n    try { if (typeof gtag === 'function') { var p = params || {}; p.article = meta.slug; gtag('event', name, p); } } catch (e) {}\n  }\n  function jumpList(missed){\n    if (!missed.length) { return ''; }\n    return '<ul class=\"msq-jump\">' + missed.map(function(q){\n      return '<li><a href=\"' + q.getAttribute('data-section') + '\">' + q.getAttribute('data-title') + '<\/a><\/li>';\n    }).join('') + '<\/ul>';\n  }\n  function emailForm(){\n    return '<div class=\"msq-sub\"><p><strong>Get the next one.<\/strong> We publish new articles on ' + meta.category\n      + ' most weeks and recheck this page on Sundays. Email me when a new article goes up or this page changes.<\/p>'\n      + '<form class=\"msq-form\" method=\"post\" action=\"\/mail\/form.php\" novalidate>'\n      + '<input type=\"hidden\" name=\"list\" value=\"' + meta.list + '\">'\n      + '<input type=\"hidden\" name=\"name\" value=\"\">'\n      + '<label class=\"msq-hp\" aria-hidden=\"true\">Leave this empty<input type=\"text\" name=\"website\" tabindex=\"-1\" autocomplete=\"off\"><\/label>'\n      + '<input type=\"email\" name=\"email\" placeholder=\"you@example.com\" required aria-label=\"Email address\" autocomplete=\"email\">'\n      + '<button type=\"submit\" class=\"msq-btn\">Email me the updates<\/button>'\n      + '<a href=\"#\" class=\"msq-no\">No thanks<\/a>'\n      + '<p class=\"msq-privacy\">We store your email and this page\\'s topic, nothing else. Unsubscribe any time.<\/p>'\n      + '<\/form><p class=\"msq-msg\" aria-live=\"polite\"><\/p><\/div>';\n  }\n  \/* The autoresponder always answers 200 with its own page. A \".msg.err\" box means the\n     address was rejected, \"You're subscribed\" means accepted, and a redirect only happens\n     after a successful subscribe. Same reading as the landing pages on the other sites. *\/\n  function sendForm(form){\n    return fetch(form.getAttribute('action'), { method: 'POST', body: new FormData(form), credentials: 'same-origin', redirect: 'manual' })\n      .then(function(res){\n        if (res.type === 'opaqueredirect') { return { status: 'ok' }; }\n        if (res.status === 404) { return { status: 'notlive' }; }\n        if (!res.ok) { throw new Error('HTTP ' + res.status); }\n        return res.text().then(function(t){\n          var doc = new DOMParser().parseFromString(t, 'text\/html');\n          var err = doc.querySelector('.msg.err');\n          if (err) {\n            var m = err.textContent.trim();\n            if (\/something went wrong\/i.test(m)) { throw new Error(m); }\n            return { status: 'rejected', message: m };\n          }\n          if (\/you.re subscribed\/i.test(doc.body.textContent)) { return { status: 'ok' }; }\n          return { status: 'unknown' };\n        });\n      });\n  }\n  function wireForm(sub){\n    var form = qs(sub, '.msq-form'), msg = qs(sub, '.msq-msg');\n    qs(form, '.msq-no').addEventListener('click', function(e){\n      e.preventDefault();\n      sub.innerHTML = '<p class=\"msq-msg\">No problem. The Sunday refresh keeps this page current either way.<\/p>';\n      track('quiz_email', { result: 'declined' });\n    });\n    form.addEventListener('submit', function(e){\n      e.preventDefault();\n      var input = qs(form, 'input[name=email]'), btn = qs(form, '.msq-btn');\n      var email = input.value.trim(); input.value = email;\n      if (!\/^[^\\s@]+@[^\\s@]+\\.[^\\s@]+$\/.test(email)) { msg.textContent = 'That email does not look right.'; return; }\n      btn.disabled = true; btn.textContent = 'Sending';\n      function reset(){ btn.disabled = false; btn.textContent = 'Email me the updates'; }\n      sendForm(form).then(function(r){\n        if (r.status === 'ok' || r.status === 'unknown') {\n          sub.innerHTML = '<p class=\"msq-msg\"><strong>Done.<\/strong> We will email you when the next article on ' + meta.category\n            + ' goes up and when this page changes. If a confirmation email arrives, click it.<\/p>';\n          track('quiz_email', { result: r.status });\n          if (r.status === 'ok') { track('generate_lead', { method: 'quiz' }); }\n        } else if (r.status === 'notlive') {\n          msg.textContent = 'Sign up is not switched on yet for this site. Nothing was stored.'; reset();\n          track('quiz_email', { result: 'notlive' });\n        } else {\n          msg.textContent = r.message || 'Please check the email address and try again.'; reset();\n          track('quiz_email', { result: 'rejected' });\n        }\n      }).catch(function(){\n        msg.textContent = 'Could not reach the sign up service just now. Nothing was stored.'; reset();\n        track('quiz_email', { result: 'error' });\n      });\n    });\n  }\n  function finish(container, mode, score, total, missed){\n    var result = qs(container, '.msq-result');\n    track('quiz_complete', { mode: mode, score: score, total: total });\n    var h;\n    if (mode === 'pre') {\n      h = '<h3>You knew ' + score + ' of ' + total + ' before reading.<\/h3>';\n      h += (score === total) ? '<p>All of them. Read on anyway; the sections below carry the detail behind each answer.<\/p>'\n                             : '<p>The rest is below. Jump straight to what you missed:<\/p>' + jumpList(missed);\n      try { sessionStorage.setItem('msq-pre-' + meta.slug, String(score)); } catch (e) {}\n    } else {\n      var pre = null;\n      try { pre = sessionStorage.getItem('msq-pre-' + meta.slug); } catch (e) {}\n      h = '<h3>You got ' + score + ' of ' + total + '.<\/h3>';\n      if (pre !== null) { h += '<p>Before reading you had ' + pre + ' of ' + total + '.<\/p>'; }\n      if (missed.length) { h += '<p>Worth a second look:<\/p>' + jumpList(missed); }\n      h += emailForm();\n    }\n    result.innerHTML = h; result.hidden = false;\n    if (mode !== 'pre') { wireForm(qs(result, '.msq-sub')); }\n    result.scrollIntoView({ behavior: 'smooth', block: 'nearest' });\n  }\n  function setup(container, mode){\n    var qEls = qsa(container, '.msq-q'), answered = 0, score = 0, missed = [];\n    qEls.forEach(function(q){\n      var answer = q.getAttribute('data-answer'), opts = qsa(q, '.msq-opt'), explain = qs(q, '.msq-explain');\n      q.removeAttribute('data-done'); explain.hidden = true; qs(explain, '.msq-verdict').textContent = '';\n      opts.forEach(function(b){ b.disabled = false; b.classList.remove('is-right', 'is-wrong'); });\n      opts.forEach(function(b){\n        b.addEventListener('click', function(){\n          if (q.getAttribute('data-done')) { return; }\n          q.setAttribute('data-done', '1');\n          var ok = b.getAttribute('data-opt') === answer;\n          opts.forEach(function(o){ o.disabled = true; if (o.getAttribute('data-opt') === answer) { o.classList.add('is-right'); } });\n          if (ok) { score += 1; } else { b.classList.add('is-wrong'); missed.push(q); }\n          qs(explain, '.msq-verdict').textContent = ok ? 'Right. ' : 'Not quite. ';\n          explain.hidden = false;\n          answered += 1;\n          track('quiz_answer', { mode: mode, question: q.getAttribute('data-q'), correct: ok ? 1 : 0 });\n          if (answered === qEls.length) { finish(container, mode, score, qEls.length, missed); }\n        });\n      });\n    });\n  }\n  var box = qs(root, '.msq-box');\n  setup(root, 'pre');\n  if (box) { box.addEventListener('toggle', function(){ if (box.open) { track('quiz_open', { mode: 'pre' }); } }); }\n  \/* The end block sits far below this script, so it does not exist yet while this runs\n     during parsing. A delegated listener finds it at click time. *\/\n  document.addEventListener('click', function(e){\n    var startBtn = (e.target && e.target.closest) ? e.target.closest('.msq-start-test') : null;\n    if (!startBtn) { return; }\n    var end = startBtn.closest('.msq-end');\n    if (!end) { return; }\n    var mount = qs(end, '.msq-mount');\n    var clone = qs(root, '.msq-body').cloneNode(true);\n    var intro = qs(clone, '.msq-intro');\n    if (intro) { intro.textContent = 'The same five questions, now that you have read the page.'; }\n    var res = qs(clone, '.msq-result'); if (res) { res.hidden = true; res.innerHTML = ''; }\n    mount.innerHTML = ''; mount.appendChild(clone);\n    setup(mount, 'test');\n    startBtn.hidden = true;\n    track('quiz_open', { mode: 'test' });\n    mount.scrollIntoView({ behavior: 'smooth', block: 'start' });\n    var first = qs(mount, '.msq-opt'); if (first) { first.focus({ preventScroll: true }); }\n  });\n  \/* Shared tool behaviour: checklists remember their ticks on this device, and a chooser\n     shows the result for the option picked. Calculators carry their own small script. *\/\n  function initTools(){\n    qsa(document, '.msq-check').forEach(function(box){\n      var key = 'msq-check-' + meta.slug + '-' + (box.getAttribute('data-id') || 'x');\n      var boxes = qsa(box, 'input[type=checkbox]'), count = qs(box, '.msq-check-count');\n      var yes = qs(box, '.msq-verdict-yes'), no = qs(box, '.msq-verdict-no');\n      var saved = {};\n      try { saved = JSON.parse(localStorage.getItem(key) || '{}'); } catch (e) {}\n      boxes.forEach(function(cb, i){ if (saved[i]) { cb.checked = true; } });\n      function refresh(){\n        var n = boxes.filter(function(cb){ return cb.checked; }).length, state = {};\n        boxes.forEach(function(cb, i){ if (cb.checked) { state[i] = 1; } });\n        try { localStorage.setItem(key, JSON.stringify(state)); } catch (e) {}\n        if (count) { count.textContent = n + ' of ' + boxes.length + (box.getAttribute('data-verb') || ' done'); }\n        if (yes && no) { yes.hidden = n === 0; no.hidden = n !== 0; }\n      }\n      boxes.forEach(function(cb){ cb.addEventListener('change', function(){ refresh(); track('tool_check', { tool: box.getAttribute('data-id') }); }); });\n      refresh();\n    });\n    qsa(document, '.msq-choose').forEach(function(box){\n      var results = qsa(box, '.msq-choice-result');\n      qsa(box, 'input[type=radio]').forEach(function(r){\n        r.addEventListener('change', function(){\n          results.forEach(function(el){ el.hidden = el.getAttribute('data-for') !== r.value; });\n          track('tool_choose', { tool: box.getAttribute('data-id'), choice: r.value });\n        });\n      });\n    });\n  }\n  \/\/ read progress: how far down the article the reader has scrolled, fired once per quarter\n  (function(){\n    var art = root.closest('article') || root.parentNode, fired = {};\n    function check(){\n      var top = art.getBoundingClientRect().top + window.pageYOffset, h = art.offsetHeight || 1;\n      var seen = (window.pageYOffset + window.innerHeight - top) \/ h * 100;\n      [25, 50, 75, 100].forEach(function(m){ if (seen >= m && !fired[m]) { fired[m] = true; track('read_progress', { percent: m }); } });\n    }\n    window.addEventListener('scroll', check, { passive: true }); window.addEventListener('load', check);\n  })();\n  if (document.readyState === 'loading') { document.addEventListener('DOMContentLoaded', initTools); } else { initTools(); }\n})();<\/script>\n<\/div>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"what-are-the-real-ways-to-know-my-body-fat-percentage\">What are the real ways to know my body fat percentage?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The methods a person can actually reach fall into three groups: formulas that measure nothing, devices that measure something related to fat and model the rest, and scans that image the body directly. Most articles list them. Almost none say how far each one can be from the answer, which is the only column that changes what you do next. Here is that column, compiled from the studies that measured it, in percentage points of body fat unless a row says otherwise.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table><thead><tr><th>Method<\/th><th>What it actually measures<\/th><th>How far the estimate can sit from a reference<\/th><th>Source<\/th><\/tr><\/thead><tbody><tr><td>Estimate from BMI<\/td><td>Nothing. It is height and weight put through an equation.<\/td><td>Standard error of estimate of 4.1 percentage points in adults, in the study that produced the formula<\/td><td><a href=\"https:\/\/pubmed.ncbi.nlm.nih.gov\/2043597\/\" target=\"_blank\" rel=\"noopener\">Deurenberg, British Journal of Nutrition, 1991<\/a><\/td><\/tr><tr><td>Consumer impedance scale, foot to foot<\/td><td>Weight, plus resistance to a small current through the legs<\/td><td>Across fifteen devices, constant error against a four compartment reference ran from 3.5 points low to 11.7 points high<\/td><td><a href=\"https:\/\/www.cambridge.org\/core\/journals\/british-journal-of-nutrition\/article\/assessing-the-reliability-and-crosssectional-and-longitudinal-validity-of-fifteen-bioelectrical-impedance-analysis-devices\/EC129A8C9BE88D77DE09A7B8DF400936\" target=\"_blank\" rel=\"noopener\">Fifteen device comparison, British Journal of Nutrition<\/a><\/td><\/tr><tr><td>Multi frequency impedance, hand to foot<\/td><td>Weight, plus resistance at several frequencies through the whole body<\/td><td>Mean bias of 2.54 points against a scan, with individual readings spread from 2.67 points low to 7.74 points high<\/td><td><a href=\"https:\/\/www.frontiersin.org\/journals\/analytical-science\/articles\/10.3389\/frans.2026.1767078\/full\" target=\"_blank\" rel=\"noopener\">148 Malaysian adults, Frontiers in Analytical Science<\/a><\/td><\/tr><tr><td>Skinfold calipers<\/td><td>The thickness of a pinch of skin and fat at set sites<\/td><td>Depends on who is holding them. Expert measurement error stayed under the 5 percent limit; a novice went over 7.5 percent at the abdomen and hip<\/td><td><a href=\"https:\/\/doi.org\/10.1007\/s11332-025-01389-8\" target=\"_blank\" rel=\"noopener\">Expert versus novice raters, Sport Sciences for Health<\/a><\/td><\/tr><tr><td>Tape measure, circumference formula<\/td><td>Neck, waist and hip girths<\/td><td>Reported standard error of 3 to 4 points, running low in men and high in women<\/td><td><a href=\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC9008774\/\" target=\"_blank\" rel=\"noopener\">Marine Corps body composition survey<\/a><\/td><\/tr><tr><td>Air displacement, the pod<\/td><td>Body volume, converted to fat using an assumed density<\/td><td>Reported to underestimate by roughly 2 to 3 points against multi compartment models<\/td><td><a href=\"https:\/\/www.sciencedirect.com\/science\/article\/pii\/S0002916523061427\" target=\"_blank\" rel=\"noopener\">Air displacement review, American Journal of Clinical Nutrition<\/a><\/td><\/tr><tr><td>DXA scan<\/td><td>How two X-ray energies pass through tissue, region by region<\/td><td>The practical reference, not the truth. Repeat scans reported between 0.7 and 2.6 percent variation, and two manufacturers read about 1.4 points apart on the same person<\/td><td><a href=\"https:\/\/onlinelibrary.wiley.com\/doi\/full\/10.1002\/oby.22108\" target=\"_blank\" rel=\"noopener\">Precision study<\/a> and <a href=\"https:\/\/pubmed.ncbi.nlm.nih.gov\/41986464\/\" target=\"_blank\" rel=\"noopener\">device conversion study<\/a><\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Two things fall out of that table. The estimate from BMI is not a measurement at all: the <a href=\"https:\/\/www.cdc.gov\/bmi\/adult-calculator\/index.html\" target=\"_blank\" rel=\"noopener\">CDC<\/a> describes BMI as a calculated measure of weight relative to height, and the equation that converts it to body fat shipped with a standard error of about four points. And even the reference method has a range. Nobody here is handing out the truth, only estimates with different error bars, and the honest ones say so.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1600\" height=\"900\" src=\"https:\/\/metaboliboost.com\/articles\/wp-content\/uploads\/2026\/09\/how-to-know-my-body-fat-percentage-chart.png\" alt=\"Chart on how to know my body fat percentage: error of each method from 1.4 points for DXA differences to 11.7 for the worst consumer scale.\" class=\"wp-image-2186\" srcset=\"https:\/\/metaboliboost.com\/articles\/wp-content\/uploads\/2026\/09\/how-to-know-my-body-fat-percentage-chart.png 1600w, https:\/\/metaboliboost.com\/articles\/wp-content\/uploads\/2026\/09\/how-to-know-my-body-fat-percentage-chart-300x169.png 300w, https:\/\/metaboliboost.com\/articles\/wp-content\/uploads\/2026\/09\/how-to-know-my-body-fat-percentage-chart-1024x576.png 1024w, https:\/\/metaboliboost.com\/articles\/wp-content\/uploads\/2026\/09\/how-to-know-my-body-fat-percentage-chart-768x432.png 768w, https:\/\/metaboliboost.com\/articles\/wp-content\/uploads\/2026\/09\/how-to-know-my-body-fat-percentage-chart-1536x864.png 1536w\" sizes=\"auto, (max-width: 1600px) 100vw, 1600px\" \/><figcaption class=\"wp-block-image__caption\">Percentage points of body fat, from the studies in the table above. Each row measures a different kind of error, so read the labels; the point is that nobody is handing out the truth, only estimates with different error bars.<\/figcaption><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"why-does-the-number-on-my-bathroom-scale-move-so-much\">Why does the number on my bathroom scale move so much?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">A consumer impedance scale has exactly two real inputs. It weighs you, and it sends a small current up one leg and down the other to measure resistance. Fat mass, muscle mass, bone mass and that alarming visceral fat figure are all modelled from those two numbers by an equation fitted to a reference group of people. If you are not much like that reference group, the model is guessing politely.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Resistance depends on water, so anything that moves your water moves the reading: a large drink, a salty dinner, a session that leaves you a litre down in sweat. That part is well known. The odd result that turns up when researchers test these devices properly is not.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A <a href=\"https:\/\/www.cambridge.org\/core\/journals\/british-journal-of-nutrition\/article\/assessing-the-reliability-and-crosssectional-and-longitudinal-validity-of-fifteen-bioelectrical-impedance-analysis-devices\/EC129A8C9BE88D77DE09A7B8DF400936\" target=\"_blank\" rel=\"noopener\">British Journal of Nutrition study of fifteen impedance devices<\/a> put 73 adults through every one of them and compared the output with a four compartment reference model. The repeatability was excellent: precision error ran from 0.0 to 0.49 percentage points. The accuracy was not. Constant error against the reference ran from 3.5 points low to 11.7 points high depending on the device. Precise and correct are not the same property, and a scale can be one without being the other.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The detail worth stealing from that paper is what the authors said about five of the foot to foot devices, which reported precision between 0.0 and 0.11 points. They flagged it as suspicious, suggesting the algorithm may simply be restricting how much the output is allowed to vary. A scale that never disagrees with itself is not being careful. It is being quiet. And a device that will not move cannot show you a change either.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"540\" height=\"360\" src=\"https:\/\/metaboliboost.com\/articles\/wp-content\/uploads\/2026\/09\/d.jpg\" alt=\"Clinician showing a patient results on a tablet, the assessment route for anyone asking how to know my body fat percentage\" class=\"wp-image-2017\" srcset=\"https:\/\/metaboliboost.com\/articles\/wp-content\/uploads\/2026\/09\/d.jpg 540w, https:\/\/metaboliboost.com\/articles\/wp-content\/uploads\/2026\/09\/d-300x200.jpg 300w\" sizes=\"auto, (max-width: 540px) 100vw, 540px\" \/><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"how-much-does-the-number-have-to-move-before-the-change-is-r\">How much does the number have to move before the change is real?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">This is the question nobody answers, and it has a standard formula. Bone density clinics use <a href=\"https:\/\/pubmed.ncbi.nlm.nih.gov\/17616413\/\" target=\"_blank\" rel=\"noopener\">least significant change<\/a>, which is 2.77 times the precision error of the instrument. Below that, a change is measurement noise at 95 percent confidence. Above it, something real probably happened. The same arithmetic works on any body composition tool, if you can find its precision error.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Run it on the numbers above. A scale with a precision error of 0.49 percentage points gives 2.77 times 0.49, which is about 1.4 points. So a reading that drifts from 28.0 to 28.9 has told you nothing. A drift to 29.6 is probably real. Run it on the DXA figures and the units change, because scan precision is reported as a percentage of the fat mass measured rather than in percentage points: at the reported 0.7 to 2.6 percent variation, a person carrying 25 kg of fat needs roughly 0.5 to 1.8 kg of change before the scan can see it.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The catch is why this calculation almost never gets run. No consumer scale manufacturer publishes a precision error, so the one number the sum needs is the one nobody prints on the box. Independent studies are the only place it exists.<\/p>\n\n\n\n<div class=\"msq-tool\" id=\"ms-lsc-calc\">\n<h3>Is the change real, or is it noise?<\/h3>\n<p>The least significant change formula from this page: 2.77 times the precision error of the instrument. Enter two readings and the precision error, and the tool says whether the difference clears it at 95 percent confidence.<\/p>\n<div class=\"msq-calc\">\n<label>Earlier reading, percent body fat<input type=\"number\" id=\"lsc-a\" value=\"28.0\" min=\"1\" max=\"70\" step=\"0.1\"><\/label>\n<label>Later reading, percent body fat<input type=\"number\" id=\"lsc-b\" value=\"28.9\" min=\"1\" max=\"70\" step=\"0.1\"><\/label>\n<label>Precision error of the device, percentage points<input type=\"number\" id=\"lsc-p\" value=\"0.49\" min=\"0.01\" max=\"10\" step=\"0.01\"><\/label>\n<div class=\"msq-calc-out\" id=\"lsc-out\"><\/div>\n<\/div>\n<p class=\"msq-note\">0.49 is the largest precision error measured across fifteen consumer impedance devices in the study on this page; no consumer manufacturer publishes its own. Precise and correct are different properties: this tells you whether the device moved, not whether it is right.<\/p>\n<\/div>\n<script>\n(function(){\n  var a = document.getElementById('lsc-a'), b = document.getElementById('lsc-b'), p = document.getElementById('lsc-p'), out = document.getElementById('lsc-out');\n  if (!out) { return; }\n  function run(){\n    var x = parseFloat(a.value), y = parseFloat(b.value), pe = parseFloat(p.value);\n    if (isNaN(x) || isNaN(y) || isNaN(pe)) { out.textContent = 'Enter two readings and a precision error.'; return; }\n    var lsc = 2.77 * pe, diff = Math.abs(y - x);\n    var msg = '<strong>Least significant change: ' + lsc.toFixed(2) + ' percentage points.<\/strong> Your readings differ by ' + diff.toFixed(2) + '. ';\n    msg += (diff > lsc) ? 'That clears the threshold, so something real probably happened, on this device.' : 'That is inside the threshold: measurement noise at 95 percent confidence, and the device has told you nothing yet.';\n    out.innerHTML = msg;\n    try { if (typeof gtag === 'function') { gtag('event', 'tool_calc', { tool: 'lsc-calc', article: 'how-to-know-my-body-fat-percentage' }); } } catch (e) {}\n  }\n  [a, b, p].forEach(function(el){ el.addEventListener('input', run); el.addEventListener('change', run); });\n  run();\n})();\n<\/script>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"what-do-people-who-compared-a-scan-with-a-scale-actually-rep\">What do people who compared a scan with a scale actually report?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">I read the review pages for four body composition companies on Trustpilot and three threads in the r\/loseit community, and pulled every account naming a body fat figure or a direct comparison. Six were specific enough to use. These are accounts, not evidence: nobody here had their measurement audited, and none of it is a finding about how these devices perform in general.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">On <a href=\"https:\/\/www.trustpilot.com\/review\/www.withings.com\" target=\"_blank\" rel=\"noopener\">Trustpilot<\/a>, a reviewer posting as Karol B wrote on 28 August 2026 that a scan had put them at 17 percent while their scale kept showing 11, and objected to the manufacturer advertising a 99 percent correlation with DXA. On the same page, a reviewer posting as Jame Humie wrote on 5 September 2026 that the readings swung from 4.6 percent one day to 9.4 percent the next, and went back to calipers. On <a href=\"https:\/\/www.trustpilot.com\/review\/oxiline.shop\" target=\"_blank\" rel=\"noopener\">another brand page<\/a>, a reviewer posting as LRP wrote on 29 July 2026 that the scale sat about 7 points above a scan and called impedance measurement misleading.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In an r\/loseit thread from June 2026 about <a href=\"https:\/\/www.reddit.com\/r\/loseit\/comments\/1tv7u82\/experience_comparing_dexa_scan_results_to_home\/\" target=\"_blank\" rel=\"noopener\">comparing scans with home scales<\/a>, a commenter posting as Yummytastic argued that scales which look consistent often achieve it through algorithm tricks that restrict the output range, and that the extra steadiness is theatre rather than accuracy. That is a stranger on the internet arriving independently at the same conclusion the fifteen device study reached, which is not proof of anything but is a coincidence worth noticing. In the same thread, a commenter posting as Strategic_Sage said they had stopped using body fat figures at all and tracked weight, tape measurements and gym performance instead.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The accounts that cut the other way matter as much. In a <a href=\"https:\/\/www.reddit.com\/r\/loseit\/comments\/1nowg8g\/smart_scale_vs_dexa_results_data\/\" target=\"_blank\" rel=\"noopener\">September 2025 thread<\/a>, a poster comparing a foot to foot scale with their first scan found the body fat figures landed within about two points of each other and the fat free mass within a few pounds, and said they would not tell anyone to bin their scale on that evidence. Their scale was badly wrong on visceral fat, reporting a figure many times what the scan gave. In the same thread, a commenter posting as CuteAmoeba9876 reported the opposite experience: across a year of lifting, dropping weight and losing two trouser sizes, their scale moved the body fat figure by a single point, so they threw it out.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The six together sit with the studies rather than against them. They agree on direction: the scale is a rough locator. They disagree on how rough, one within two points and one seven points out, which is about the spread the fifteen device comparison measured. Nobody in these accounts could tell in advance which of the two they would be.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"is-a-dxa-scan-worth-paying-for\">Is a DXA scan worth paying for?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">It depends what you want from it. As a one off picture of where fat sits and how much lean mass you carry, a scan tells you things no scale can. The <a href=\"https:\/\/www.bhf.org.uk\/informationsupport\/heart-matters-magazine\/nutrition\/weight\/best-way-to-measure-body-fat\" target=\"_blank\" rel=\"noopener\">British Heart Foundation<\/a> puts a UK DEXA scan at least 100 pounds and an air displacement pod from about 40 pounds, and a reviewer of a US scanning service quoted 60 dollars on 3 September 2026. Affordable once, expensive as a habit.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">As a way of tracking change, a scan has one rule that is easy to break. Machines from different manufacturers have been <a href=\"https:\/\/pubmed.ncbi.nlm.nih.gov\/41986464\/\" target=\"_blank\" rel=\"noopener\">reported to read about 1.4 percentage points apart<\/a> on the same person, because calibration and algorithms are proprietary and differ. Compare one clinic with another and part of the difference belongs to the hardware. Same machine, or no comparison.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">One thing to hold separately from all of the arithmetic. If watching this number is causing distress, or driving eating patterns that worry you or the people around you, that is worth raising with a doctor or a registered dietitian. Measurement accuracy is not the relevant problem in that situation, and no figure from any device is.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"what-is-worth-tracking-instead\">What is worth tracking instead?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Not that measurement is hopeless. A trend from one consistent method beats a single precise sounding number from any of them. Pick one tool, use it under the same conditions every time, and read it over weeks rather than days.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1376\" height=\"768\" src=\"https:\/\/metaboliboost.com\/articles\/wp-content\/uploads\/2026\/09\/healthy-habits-how-to-know-my-body-fat-percentage.jpg\" alt=\"A woman enjoys a healthy green smoothie, focusing on habits instead of how to know my body fat percentage.\" class=\"wp-image-2037\" srcset=\"https:\/\/metaboliboost.com\/articles\/wp-content\/uploads\/2026\/09\/healthy-habits-how-to-know-my-body-fat-percentage.jpg 1376w, https:\/\/metaboliboost.com\/articles\/wp-content\/uploads\/2026\/09\/healthy-habits-how-to-know-my-body-fat-percentage-300x167.jpg 300w, https:\/\/metaboliboost.com\/articles\/wp-content\/uploads\/2026\/09\/healthy-habits-how-to-know-my-body-fat-percentage-1024x572.jpg 1024w, https:\/\/metaboliboost.com\/articles\/wp-content\/uploads\/2026\/09\/healthy-habits-how-to-know-my-body-fat-percentage-768x429.jpg 768w\" sizes=\"auto, (max-width: 1376px) 100vw, 1376px\" \/><figcaption class=\"wp-block-image__caption\">Tracking daily habits and energy levels often proves more valuable than scale numbers.<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Alongside it, track what can be measured well. Weight is one: the only figure a home scale measures directly rather than models, and accurate to grams. Waist to height ratio needs only a tape, is flagged by the British Heart Foundation as a useful alternative, and speaks to where fat sits rather than how much there is. It is only as good as the placement, though, and our guide to <a href=\"https:\/\/metaboliboost.com\/articles\/how-to-take-measurements-for-weight-loss\/\">taking body measurements the same way every time<\/a> sets out where the published protocols put the tape and why they disagree. Strength in the gym and how clothes fit are crude, but they do not drift with hydration, which is more than the impedance figure can claim. Our note on <a href=\"https:\/\/metaboliboost.com\/articles\/what-is-more-important-weight-loss-or-fat-loss-2\/\">weight loss versus fat loss<\/a> works through which of these answers which question.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Two other pieces here are worth reading beside this one. Differences in how men and women carry fat explain part of why the same device errs in opposite directions by sex, covered in <a href=\"https:\/\/metaboliboost.com\/articles\/why-its-easier-for-men-to-lose-weight-the-role-of-testosterone-and-body-fat\/\">the role of testosterone and body fat<\/a>. And if your figure has stopped moving despite everything going right, <a href=\"https:\/\/metaboliboost.com\/articles\/why-the-last-5-7-kg-is-the-hardest-to-lose-the-real-science-behind-stubborn-fat\/\">why the last few kilograms are the hardest<\/a> deals with the physiology rather than the measurement.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"frequently-asked-questions\">Frequently asked questions<\/h2>\n\n\n<div id=\"rank-math-faq\" class=\"rank-math-block\">\n<div class=\"rank-math-list \">\n<div id=\"faq-q-1\" class=\"rank-math-list-item\">\n<h3 class=\"rank-math-question \">Does drinking water or eating before I step on a body fat scale change the reading?<\/h3>\n<div class=\"rank-math-answer \">\n\n<p>Yes, because an impedance scale infers body composition from resistance to a current, and water conducts. A drink, a meal or a sweaty session all shift the resistance and therefore the estimate. Measuring under identical conditions every time will not make the number accurate, but it does remove one source of the day to day swing.<\/p>\n\n<\/div>\n<\/div>\n<div id=\"faq-q-2\" class=\"rank-math-list-item\">\n<h3 class=\"rank-math-question \">Why do two body fat scales in the same house give different numbers?<\/h3>\n<div class=\"rank-math-answer \">\n\n<p>Because each brand uses its own equation, fitted to its own reference group. The study of fifteen impedance devices found their constant error against a reference model ran from 3.5 points low to 11.7 points high, so two devices could disagree by more than ten points on the same person without either one being broken.<\/p>\n\n<\/div>\n<\/div>\n<div id=\"faq-q-3\" class=\"rank-math-list-item\">\n<h3 class=\"rank-math-question \">Can I work out my body fat percentage from my BMI?<\/h3>\n<div class=\"rank-math-answer \">\n\n<p>You can run the number, but it is a prediction rather than a measurement. The original adult equation was published with a standard error of estimate of 4.1 percentage points, meaning a typical prediction misses by around four points in either direction. That is wider than most of the changes people are trying to detect.<\/p>\n\n<\/div>\n<\/div>\n<div id=\"faq-q-4\" class=\"rank-math-list-item\">\n<h3 class=\"rank-math-question \">Do skinfold calipers work if I pinch myself?<\/h3>\n<div class=\"rank-math-answer \">\n\n<p>Self measurement removes the biggest advantage calipers have, which is a trained hand doing the same thing at the same site every time. Research comparing experienced and inexperienced raters found the novice exceeded the accepted error limit at the abdomen and hip, and several sites on the back and trunk are impossible to reach on yourself.<\/p>\n\n<\/div>\n<\/div>\n<div id=\"faq-q-5\" class=\"rank-math-list-item\">\n<h3 class=\"rank-math-question \">Is the visceral fat figure on my scale worth anything?<\/h3>\n<div class=\"rank-math-answer \">\n\n<p>Treat it as the least reliable figure on the display. It is modelled from weight and one resistance reading rather than measured, and it is the number that forum posts comparing scales with scans most often report as wildly off. A tape measure around the waist gives you more for less.<\/p>\n\n<\/div>\n<\/div>\n<div id=\"faq-q-6\" class=\"rank-math-list-item\">\n<h3 class=\"rank-math-question \">Should I throw my body fat scale away?<\/h3>\n<div class=\"rank-math-answer \">\n\n<p>Not necessarily. A scale that repeats well is a reasonable trend tracker even when the absolute figure is several points out, and the weight it reports is genuinely accurate. The mistake is treating the body fat percentage as a measurement of you rather than as a rough index that moves in roughly the right direction.<\/p>\n\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n\n\n<div class=\"msq-end\" id=\"ms-quiz-end\">\n<p><strong>Finished the page?<\/strong> The same five questions from the top, to see what stuck.<\/p>\n<button type=\"button\" class=\"msq-btn msq-start-test\">Test Your Understanding of This Article<\/button>\n<div class=\"msq-mount\"><\/div>\n<\/div>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p class=\"wp-block-paragraph\"><em>This article is general information, not medical advice, and is not a substitute for care from a qualified healthcare professional. Speak to your doctor about your own situation.<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Every way of estimating body fat carries an error range. Here is that range for each method, and how much a reading has to move before it means anything.<\/p>\n","protected":false},"author":1,"featured_media":2006,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":"","rank_math_title":"How to Know My Body Fat Percentage: How Wrong Each Method Is","rank_math_description":"How to know my body fat percentage honestly: what each method measures, how far off it can be, and why a trend beats any single reading.","rank_math_focus_keyword":"how to know my body fat percentage","rank_math_canonical_url":"","rank_math_breadcrumb_title":"","rank_math_facebook_title":"","rank_math_facebook_description":"","rank_math_facebook_image":"","rank_math_twitter_title":"","rank_math_twitter_description":"","rank_math_twitter_image":"","rank_math_pillar_content":"","rank_math_robots":[],"rank_math_advanced_robots":[]},"categories":[23],"tags":[],"class_list":["post-2009","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-metabolism"],"_links":{"self":[{"href":"https:\/\/metaboliboost.com\/articles\/wp-json\/wp\/v2\/posts\/2009","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/metaboliboost.com\/articles\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/metaboliboost.com\/articles\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/metaboliboost.com\/articles\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/metaboliboost.com\/articles\/wp-json\/wp\/v2\/comments?post=2009"}],"version-history":[{"count":9,"href":"https:\/\/metaboliboost.com\/articles\/wp-json\/wp\/v2\/posts\/2009\/revisions"}],"predecessor-version":[{"id":2272,"href":"https:\/\/metaboliboost.com\/articles\/wp-json\/wp\/v2\/posts\/2009\/revisions\/2272"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/metaboliboost.com\/articles\/wp-json\/wp\/v2\/media\/2006"}],"wp:attachment":[{"href":"https:\/\/metaboliboost.com\/articles\/wp-json\/wp\/v2\/media?parent=2009"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/metaboliboost.com\/articles\/wp-json\/wp\/v2\/categories?post=2009"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/metaboliboost.com\/articles\/wp-json\/wp\/v2\/tags?post=2009"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}