Lean body mass calculator: Boer, James and Hume compared

Lean body mass at 80 kg and 180 cmworked example

60.6 kg

Boer 1984: 61.42 kgthe most widely cited
James 1976: 62.72 kgthe only non-linear one
Hume 1966: 57.79 kgthe earliest of the three
How far apart they are: 4.93 kgabout 8.1% of lean mass
Fat-free mass index at the midpoint: 18.7 kg/m2

The headline figure is the midpoint of three published equations, not one of them dressed up as the answer. They were derived in different cohorts against different reference methods, and here they land 4.93 kg apart. All three know only your height, weight and sex, so two people of the same dimensions get the same number however that mass is actually distributed.

Realistic range

57.79 kg to 62.72 kg

The spread between equations is a floor on the uncertainty, not the whole of it: all three share the same blindness to how mass is distributed, so they can agree with each other and still be some distance from a scan.

Weightkg, lb or stone all parse.Heightcm, m or feet and inches all parse.

Sex

Each equation has its own coefficient set.

Measured body fat percentage (optional)If you have a scan or a caliper reading, this route beats all three equations: lean mass is simply weight times one minus your fat fraction.

What each equation implies for fat mass at 80 kg
Equation	Lean mass	Fat mass	Implied body fat	Derived from
Boer (1984)	61.42 kg	18.58 kg	23.2%	derived for normalising body-fluid volumes, and the most widely cited of the three
James (1976)	62.72 kg	17.28 kg	21.6%	the only one of the three with a non-linear shape term, so it diverges fastest at the extremes
Hume (1966)	57.79 kg	22.21 kg	27.8%	the earliest of the three, against total body water

The implied body-fat column is the same arithmetic read the other way: weight minus lean mass, over weight. Notice that a 4.93 kg disagreement about lean mass is a disagreement of about six percentage points about body fat, which is why this site runs the tape method separately rather than inferring one from the other.

A lean body mass calculator estimates how much of your weight is not fat, from your height, weight and sex. It runs the Boer, James and Hume equations together rather than picking one, because at 80 kilograms and 180 centimetres they land 4.93 kilograms apart, and that spread is the honest answer.

Lean body mass (Boer) — men: LBM (kg) = 0.407 x weight(kg) + 0.267 x height(cm) - 19.2; women: LBM = 0.252 x weight + 0.473 x height - 48.3. Verified 2026-07-30 against Boer, American Journal of Physiology 1984 (Derived to normalise body-fluid volumes, not to assess athletes. It knows only your height, weight and sex, so it cannot tell a heavily muscled body from a heavier one of the same dimensions - two people at the same height and weight get the same answer regardless of how that mass is distributed.)
Lean body mass (James) — men: LBM (kg) = 1.10 x weight(kg) - 128 x (weight(kg) / height(cm))^2; women: LBM = 1.07 x weight - 148 x (weight / height)^2. Verified 2026-07-30 against James 1976 (DHSS/MRC Group report), equation as reproduced in the Br J Radiol 2022 comparison of ten lean-mass equations (The only one of the three with a non-linear shape term, so it diverges fastest from the others at the extremes of height and weight. The originating document is a 1976 government report rather than a journal paper, so the equation is verified here against its reproduction in a peer-reviewed comparison study, not against the report itself.)
Lean body mass (Hume) — men: LBM (kg) = 0.32810 x weight(kg) + 0.33929 x height(cm) - 29.5336; women: LBM = 0.29569 x weight + 0.41813 x height - 43.2933. Verified 2026-07-30 against Hume, Journal of Clinical Pathology 1966 (The earliest of the three and derived against total body water in a mid-1960s cohort, which is the likeliest reason it reads consistently lower than Boer and James at the same height and weight.)
Disagreement between published lean-mass equations — spread across Boer, James and Hume at the same height, weight and sex: commonly 2-5 kg. Verified 2026-07-30 against Br J Radiol 2022, comparison of ten predictive lean-mass equations against DXA (The spread between equations is a floor on the uncertainty, not the whole of it: all three share the same blindness to how mass is distributed, so they can agree with each other and still be some distance from a scan.)

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Frequently asked questions

How do you calculate lean body mass?

Boer 1984 for men is 0.407 times weight in kilograms plus 0.267 times height in centimetres minus 19.2. For women it is 0.252 times weight plus 0.473 times height minus 48.3. This tool also runs the James 1976 and Hume 1966 equations, which use different coefficients.

Why do the three formulas give different answers?

They were derived in different cohorts against different reference methods. At 80 kilograms and 180 centimetres for a man, Boer gives 61.42 kilograms, James 62.72 and Hume 57.79, a spread of 4.93 kilograms or about 6 percent. No equation among them is the correct one.

Which lean body mass formula is most accurate?

For an individual, none of them is measured. Boer is the most widely cited and is what many clinical dosing references use, which is the reason this tool shows it first. If you need an accurate figure rather than an estimate, that means a DXA scan, not an equation.

What is fat-free mass index?

Lean mass divided by height in metres squared, the same shape of scaling BMI uses but applied to lean mass instead of total weight. It lets you compare lean mass between people of different heights, and this tool computes it from the midpoint of the three equations.

Can I get lean body mass from my body fat percentage?

Yes, and it is a better route if you have a measured percentage: lean mass equals weight times one minus your body fat fraction. The tool does this too. An estimated body fat percentage does not improve on the equations, since it is an estimate in the same way.

Do these equations work for very muscular or very light people?

Less well. All three know only your height, weight and sex, so two people of the same dimensions get the same answer however that mass is distributed. James is the only one with a non-linear shape term, which is why it diverges fastest at the extremes.

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The next number

No body metric means much on its own. Here is what this one feeds into.

Body fat calculatorThe same split from the other direction, measured with a tape rather than inferred from height and weight.Protein calculatorProtein targets scale better with lean mass than with total weight, and this is the number they scale from.

Related calculators

Body fat calculatorBody composition Protein calculatorNutrition targets TDEE calculatorMetabolism

Every formula on this page is listed with its source on the methodology page, and changes to any reference value are logged in the data changelog. Canonical URL: https://myhealthmywellness.com/lean-body-mass-calculator