Lean Body Mass Calculator
Estimate lean body mass (LBM) with the Boer, Hume and James formulas, side by side, with the fat mass and body-fat percentage they imply and how far each was off against DXA.
Lean Body Mass Calculator
How to use the Lean Body Mass Calculator
Enter weight, height, and gender
Weight in kg, height in cm, biological gender (male/female — formulas use gender-specific constants). For best accuracy, weigh first thing in the morning + measure height barefoot against a wall.
Read the estimate and the spread
The headline is the average of the Boer (1984), Hume (1966) and James (1976) formulas, each shown separately. When they disagree by more than 5 kg the page says so: the average is then a figure none of them supports.
Use it with care for nutrition
Most protein guidance is per kg of body weight — the ISSN gives 1.4–2.0 g/kg/day for exercising adults. Helms et al.'s contest-preparation range, 2.3–3.1 g, is per kg of lean mass, so check which basis a figure uses before applying this estimate.
For a measurement, get a DXA scan
The formulas use only height, weight and sex. Against DXA in 1,558 adults aged 60–65, their 95% limits of agreement spanned 13–17 kg (Br J Radiol 2022). A DXA scan measures lean mass directly.
Lean body mass — three formulas, and how far to trust them
Lean body mass (LBM) is body weight minus fat: muscle, bone, organs and water. Measuring it takes a DXA scan or similar; estimating it from height, weight and sex takes a formula. This page uses three long-established ones — Boer (1984), Hume (1966) and James (1976) — and shows all three, because they do not agree.
The three formulas
Boer: men 0.407 × weight + 0.267 × height − 19.2; women 0.252 × weight + 0.473 × height − 48.3 (weight in kg, height in cm). Hume: men 0.32810 × weight + 0.33929 × height − 29.5336; women 0.29569 × weight + 0.41813 × height − 43.2933. James: men 1.10 × weight − 128 × (weight ÷ height)²; women 1.07 × weight − 148 × (weight ÷ height)². The two linear formulas move in step; James is quadratic in weight over height, so at a high weight for a short height it falls away from the others, sometimes by tens of kilograms.
Three formulas that agree tell you little more than one; three that disagree tell you the estimate is uncertain.
How accurate they are
A 2022 study in the British Journal of Radiology compared ten LBM equations with DXA in 747 men and 811 women aged 60 to 65. Across both sexes Boer's equation read 3.6 kg low on average, James's 4.1 kg low and Hume's 1.1 kg low; their 95% limits of agreement spanned 13.1, 14.2 and 16.9 kg. None of the three was the best performer — the Gallagher and Janmahasatian equations were — and the study covered only that age band. Read the result as an estimate with a wide margin, and use the same formula each time if you track it.
Boer, Hume and James side by side, and how far each sat from DXA
LBM = body weight − fat: muscle, bone, organs and water.
Boer (1984), Hume (1966) and James (1976) each estimate it from height, weight and sex.
Against DXA in adults aged 60–65, Boer read 3.6 kg low on average (Br J Radiol 2022).
In the same study James read 4.1 kg low and Hume 1.1 kg low.
Their 95% limits of agreement spanned 13–17 kg, so one person's estimate can be well off.
James is quadratic in weight over height and diverges from the others at heavy weights for short heights.
The page shows all three and warns when they differ by more than 5 kg.
Protein targets are usually per kg of body weight; Helms et al.'s 2.3–3.1 g range is per kg of lean mass.
In that DXA comparison the Gallagher and Janmahasatian equations did best, not these three.
A DXA scan measures lean mass directly; formulas only estimate it.
Frequently Asked Questions
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Because two people of the same weight can carry very different amounts of fat. Lean mass is used in some clinical calculations — the study this page cites was choosing an equation to normalise PET scan values — and some nutrition guidance is expressed per kg of it. A formula estimate is a starting point; it cannot see your actual build.
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None of them closely, on its own. In a 2022 DXA comparison of adults aged 60–65, Hume's equation had the smallest average error (1.1 kg low) but the widest limits of agreement (16.9 kg); Boer's read 3.6 kg low with limits spanning 13.1 kg; James's 4.1 kg low, spanning 14.2 kg. Use the one closest to the average of the three, keep using the same one, and look at the trend.
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Within a few kilograms on average, but not for any one person. Against DXA in 747 men and 811 women aged 60 to 65, their 95% limits of agreement spanned 13 to 17 kg (Br J Radiol 2022). Accuracy for younger adults, very muscular people or people at the extremes of height and weight was not tested in that study.
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Most guidance is per kg of body weight: the ISSN position stand gives 1.4–2.0 g/kg/day for exercising adults, and 2.3–3.1 g/kg/day for resistance-trained people trying to keep lean mass while eating less. Helms et al. (2014) express their contest-preparation range, 2.3–3.1 g, per kg of lean mass. Our macro calculator works per kg of body weight.
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Not reliably. They use only height, weight and sex, so any weight you gain — fat or muscle — raises the estimate, and losing fat lowers it. To see whether you are gaining muscle, pair your weight trend with a direct measurement such as DXA, or with a measure of strength.
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That depends on your goals, health and starting point, and this page does not set rules for it. The formulas cannot tell you how much of your weight is fat, so they are not a basis for choosing; a DXA scan, or advice from a doctor, dietitian or coach, is.
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Yes. Loss of muscle mass and strength with age (sarcopenia) affects mobility and independence, and a doctor or physiotherapist can assess it with measures of strength and function as well as muscle mass. A formula based on height and weight cannot detect it.
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DXA (DEXA) is the reference method in the study this page cites. Other methods estimate body composition in different ways and each has its own error; whichever you use, the same device under the same conditions gives the most useful trend. This page does not rate them.
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No. All calculations run in your browser via JavaScript. Open DevTools → Network and confirm zero outbound requests. Weight, height, gender stay on your device. Safe for personal health tracking.
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Pair with: BMI Calculator for cross-reference; Body Fat Calculator for additional body fat estimates; Waist-to-Height Ratio for cardiovascular risk; TDEE Calculator for caloric needs using LBM-based Katch-McArdle. External: DEXA scan booking via local hospitals; bioimpedance scales (Withings Body+, Omron HBF-516B, Tanita BC-587); InBody at major gym chains; skinfold caliper training resources (NASM, ACSM).
Method & sources
How it computes
Boer: men 0.407W + 0.267H - 19.2, women 0.252W + 0.473H - 48.3. Hume: men 0.32810W + 0.33929H - 29.5336, women 0.29569W + 0.41813H - 43.2933. James: men 1.10W - 128(W/H)^2, women 1.07W - 148(W/H)^2 (W kg, H cm). Headline = mean, spread shown; fat mass = weight - mean. BodyCompositionKernel.leanBodyMass, tested.
What this tool implements
- Formulas checked against Puri et al. (Br J Radiol 2022), which also gives their accuracy against DXA in 747 men and 811 women aged 60-65: Boer -3.6 kg bias (limits of agreement spanning 13.1 kg), James -4.1 kg (14.2), Hume -1.1 kg (16.9); none was the best performer. The page had said 'Boer most accurate clinically', 'Hume preferred for the elderly', 'James better at extremes' and '+/-5-10%'.
- The body-fat CATEGORY is no longer shown: a percentage derived from formulas with 13-17 kg limits of agreement does not support labelled bands, and the bands came from an unsourced chart. The protein target was given as 1.6-2.2 g per kg of LEAN mass; that range (Morton 2018) is per kg of body weight, and Helms's 2.3-3.1 g is the per-lean-mass figure.
- Removed as unsourced: DEXA, BodPod and bioimpedance accuracy and prices, the Katch-McArdle accuracy claim, '250 g/month' gains, '3-5% a decade' decline, Asian body-fat comparisons, ASEAN clinic names, and body-fat thresholds for choosing to cut or bulk.
Sources
- Puri T, et al. Comparison of ten predictive equations for estimating lean body mass with dual-energy X-ray absorptiometry in older patients. Br J Radiol. 2022 (Tables 2 and 3: Hume 1966, James 1976, Boer 1984). https://doi.org/10.1259/bjr.20210378
- Jäger R, Kerksick CM, Campbell BI, et al. International Society of Sports Nutrition position stand: protein and exercise. J Int Soc Sports Nutr. 2017;14:20. https://doi.org/10.1186/s12970-017-0177-8
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