Lean Body Mass Calculator (Boer, Hume or Your Body Fat %)
Lean mass and estimated fat from weight, height and sex, or from a known body fat %.
Inputs
- Lean mass58.05(77%)
- Fat mass16.95(23%)
- Fat mass (est.)
- 17.0 kg
- Body fat % (est.)
- 22.6%
- Lean mass as % of weight
- 77.4%
- Method
- Boer (1984)
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Lean Body Mass formula
Boer: men 0.407×W + 0.267×H − 19.2, women 0.252×W + 0.473×H − 48.3 · Hume: men 0.32810×W + 0.33929×H − 29.5336, women 0.29569×W + 0.41813×H − 43.2933 · Known body fat: LBM = W × (1 − body fat % ÷ 100) (W in kg, H in cm)
Lean body mass is everything you weigh that is not fat: muscle, bone, organs, skin and water. The exact figure needs a scan, so the two formulas here estimate it from height and weight alone. Each is a regression fitted to a group of adults — Boer in 1984, Hume in 1966 — so the coefficients encode how lean the average person of a given height and weight was in that sample. Weight and height go in as kilograms and centimetres (imperial entries are converted first), the result is in kilograms, and subtracting it from your weight gives an implied fat mass and body-fat percentage. If you already know your body fat percentage from a DEXA scan, calipers or a smart scale, that is the better route: lean mass is simply weight × (1 − body fat ÷ 100), and the page uses it in place of either formula.
Lean Body Mass worked example
A 75 kg man who is 175 cm tall, using Boer: 0.407 × 75 = 30.525, plus 0.267 × 175 = 46.725, minus 19.2, gives 58.05 kg of lean body mass — about 58.1 kg. Weight minus lean mass is 16.95 kg of fat, which is 16.95 ÷ 75 = 22.6% body fat. Hume would give 54.4 kg for the same man, because it was fitted to a different group; the spread between the two is a fair picture of how rough any height-and-weight estimate is.
Where the Lean Body Mass calculator can give the wrong answer
- Both formulas assume an average build. A heavily muscled person is leaner than the estimate and someone with little muscle is less lean; the error can be several kilograms either way. A measured body fat percentage removes that problem, which is why the page uses one when you enter it.
- The regressions were fitted to adults. For children, teenagers, pregnancy or people over about 80 the coefficients do not apply and the number should not be used for anything that matters.
- Boer and Hume disagree with each other by 2–4 kg for most people, and the implied body-fat percentage disagrees with the US Navy circumference method and with BMI-based estimates. Pick one method and stick to it when tracking a trend; do not compare a Boer figure this month with a Hume figure next month.
- At the input limits — very light, very heavy, very short or very tall — a linear formula can drift far from reality or even fall below zero, in which case the page refuses to answer rather than show a negative lean mass.
- Lean body mass is not muscle mass. Roughly half of lean mass is water, and bone and organs make up much of the rest, so a 58 kg lean mass does not mean 58 kg of muscle.
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Lean Body Mass FAQ
- If you know your body fat percentage, lean body mass is weight × (1 − body fat ÷ 100): 80 kg at 20% fat is 80 × 0.8 = 64 kg lean. If you don't, use a height-and-weight formula such as Boer's: for men 0.407 × weight (kg) + 0.267 × height (cm) − 19.2, for women 0.252 × weight + 0.473 × height − 48.3. A 75 kg, 175 cm man comes out at 58.1 kg.
- There is no single target. Lean mass depends on height, sex and how much muscle you carry, and a heavier person with the same body fat percentage has more of it. The useful comparison is lean mass as a share of weight, which is just 100 minus body fat percentage — the page shows that line so you can set it against the body-fat guidance you follow, rather than against a lean-mass number that means something different for every height.
- Neither is accurate for an individual — both are averages, and they differ by a few kilograms for the same person. Boer's 1984 sample is more recent and is the default here; Hume's 1966 formula is still quoted in clinical references, so it is offered for comparison. If the difference between them matters to your decision, you need a measurement (DEXA, calipers or bioimpedance), not a formula.
- Lean body mass is everything except fat: muscle, bone, organs, skin and water. Muscle is only part of it — a large part, but about half of lean mass is water. Gaining 2 kg of lean mass on a scan is not the same as gaining 2 kg of muscle.
- Because fat tissue needs far less protein and energy than lean tissue does, so targets set per kilogram of lean mass fit a very lean and a very heavy person better than targets per kilogram of total weight. Coaches often set protein at 1.6–2.2 g per kg of lean mass during a cut; multiply the figure here by whatever rate you follow.
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