Lean Body Mass Calculator
Estimate lean body mass — everything that is not fat — from height and weight with the Boer formula, compared with the James and Hume formulas.
Your weight minus body fat, estimated from height and weight.
How the lean body mass calculator works
Lean body mass is total weight minus fat mass: muscle, bone, organs, water. Without a scan it is estimated from height, weight and sex. The Boer formula (1984) is the one most often recommended, particularly for drug dosing; the James (1976) and Hume (1966) formulas are shown for comparison and usually land within a kilogram or two.
The implied body-fat percentage is simply (weight − lean mass) ÷ weight. For a direct estimate of body fat from tape measurements, use the body-fat calculator.
Formula: Boer — men: 0.407W + 0.267H − 19.2 · women: 0.252W + 0.473H − 48.3 (W kg, H cm)
Worked examples
| Inputs | Lean body mass (Boer) | Note |
|---|---|---|
| Man, 175 cm, 75 kg | 58.1 | about 58 kg lean, 23% fat implied |
| Woman, 165 cm, 62 kg | 45.4 | Boer for women |
| Man, 6 ft, 200 lb | 146.7 | result in pounds |
FAQFrequently asked questions
What counts as lean body mass?
Everything except stored fat: muscle, bone, organs, skin and water. It is not the same as muscle mass — muscle is roughly half of it.
Which formula is best?
Boer is the usual recommendation and the one many dosing guidelines cite. James can misbehave at very high weights; Hume is older. All three are estimates within a few kilograms of a scan.
Why does the implied body fat look wrong?
Because it is derived from an average-population formula. A muscular person's true lean mass is higher than the formula gives, so the implied fat percentage reads too high. Tape or scan methods measure fat directly.
What is lean body mass used for?
Dosing some medicines and anaesthetics, setting protein targets, and tracking training progress when you know how your fat mass is changing.
Where these figures come from
- Mifflin MD et al., "A new predictive equation for resting energy expenditure in healthy individuals", Am J Clin Nutr 1990 — the BMR equation used here
- World Health Organization — Waist circumference and waist–hip ratio (2008 expert consultation) — waist-to-hip cut-offs
- Tanaka H, Monahan KD, Seals DR, "Age-predicted maximal heart rate revisited", J Am Coll Cardiol 2001 — 208 − 0.7 × age
- Nathan DM et al., "Translating the A1C assay into estimated average glucose values" (ADAG), Diabetes Care 2008 — eAG = 28.7 × A1c − 46.7
- Mosteller RD, "Simplified calculation of body-surface area", N Engl J Med 1987 — BSA = √(height × weight / 3600)
- NHS — national health guidance
Last checked: September 2026. The equations are fixed by their published papers and do not change with tax years or regulations; the thresholds quoted in verdicts name the body that set them.