Find out how much of your weight is muscle, bone and organs rather than fat. Enter height and weight for the Boer, James and Hume estimates side by side — or add a measured body fat percentage for the exact figure — and see your lean mass, fat mass and lean percentage in pounds and kilograms.
📌 The formulas estimate lean mass from height and weight only, so they cannot tell a lean lifter from someone of the same size with more fat. Enter a measured body fat % (calipers, DEXA, smart scale) for the real figure.
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The formulas
Formula
Men (kg, cm)
Women (kg, cm)
Boer
0.407 × kg + 0.267 × cm − 19.2
0.252 × kg + 0.473 × cm − 48.3
James
1.1 × kg − 128 × (kg ÷ cm)²
1.07 × kg − 148 × (kg ÷ cm)²
Hume
0.3281 × kg + 0.33929 × cm − 29.5336
0.29569 × kg + 0.41813 × cm − 43.2933
From body fat
kg × (1 − BF%)
kg × (1 − BF%)
Worked example: man, 180 lb (81.6 kg), 5′10″ (177.8 cm). Boer: 0.407 × 81.6 + 0.267 × 177.8 − 19.2 = 61.5 kg (136 lb). James gives 62.8 kg and Hume 57.6 kg — a 5 kg spread, which is why a measured body fat percentage is worth having. At 25 % body fat the true figure is 61.2 kg, close to Boer; at 15 % it would be 69.4 kg, which no height-weight formula can detect.
Everything in your body that is not fat: muscle, bone, organs, skin, blood and water. It is what you feed with protein and what burns most of your calories, which is why protein targets, drug dosing and some fitness standards are set per pound or kilogram of lean mass rather than total weight. Typical lean mass is 70–90 % of body weight for men and 65–85 % for women.
None of the height-weight formulas can see your body composition; they predict the average person of your size. Boer (1984) is the usual default and the one used in medical dosing calculators, James works well in normal-weight adults but drifts at high BMI, and Hume is the oldest. A measured body fat percentage beats all three — enter it and the calculator uses it directly.
Lean mass = weight × (1 − body fat ÷ 100). At 180 lb and 25 % body fat: 180 × 0.75 = 135 lb lean and 45 lb fat. Calipers, a DEXA scan, a Bod Pod or a decent bioimpedance scale all give a body fat figure; the body fat calculator estimates it from tape measurements with the US Navy method.
It scales with height and frame, so the percentage is more useful than the pounds: 80 % or more lean (20 % fat or less) is fit for men, 75 % or more (25 % fat or less) for women. A 5′10″ man typically carries 130–150 lb of lean mass; a 5′5″ woman 95–110 lb. Gaining lean mass is slow — around 0.5–1 lb a month for trained lifters.
Protein intake (0.8–1.2 g per lb of lean mass), keto and cutting macros, basal metabolic rate formulas such as Katch-McArdle (370 + 21.6 × lean kg), anesthetic and chemotherapy dosing, and tracking whether weight loss is coming from fat or muscle. Re-measure every few weeks and aim for the lean number to hold steady while the fat number drops.
Cite this calculator
APACalcBrew. (2026). Lean Body Mass Calculator. https://calcbrew.com/lean-body-mass-calculator
MLA“Lean Body Mass Calculator.” CalcBrew, 2026, calcbrew.com/lean-body-mass-calculator.
Link to https://calcbrew.com/lean-body-mass-calculator. Results are estimates; cite the underlying formula or data source for academic work.