Lean Body Mass Calculator

How This Calculator Works

Lean body mass is your total body weight minus fat mass — everything else, including muscle, bone, organs, and water. Enter your gender at birth, height, and weight, and this calculator shows the estimate from three different published formulas side by side — plus their average — since no single formula is more “correct” than the others.

The Formulas

Every formula below uses the same two inputs — weight (kg) and height (cm) — with different coefficients for men and women, so the same two colors track the same two quantities across all three:

Boer (1984) — derived from a large study population and the most widely cited of the three today:

$$\vC{\text{Men: LBM}} = 0.407 \times \vA{\text{Weight}} + 0.267 \times \vB{\text{Height}} - 19.2$$ $$\vC{\text{Women: LBM}} = 0.252 \times \vA{\text{Weight}} + 0.473 \times \vB{\text{Height}} - 48.3$$

James (1976) — uses a BMI-like weight-to-height-squared ratio instead of treating height and weight as separate terms:

$$\vD{\text{Men: LBM}} = 1.10 \times \vA{\text{Weight}} - 128 \times \left(\frac{\vA{\text{Weight}}}{\vB{\text{Height}}}\right)^2$$ $$\vD{\text{Women: LBM}} = 1.07 \times \vA{\text{Weight}} - 148 \times \left(\frac{\vA{\text{Weight}}}{\vB{\text{Height}}}\right)^2$$

Hume (1966) — the oldest of the three, still frequently used in clinical medication-dosing contexts:

$$\vE{\text{Men: LBM}} = 0.3281 \times \vA{\text{Weight}} + 0.33929 \times \vB{\text{Height}} - 29.5336$$ $$\vE{\text{Women: LBM}} = 0.29569 \times \vA{\text{Weight}} + 0.41813 \times \vB{\text{Height}} - 43.2933$$

Worked Example

A 180 cm (5’11”), 80 kg man:

1. Boer: $0.407 \times \vA{80} + 0.267 \times \vB{180} - 19.2 = \vC{61.4} \text{ kg}$
2. James: $1.10 \times \vA{80} - 128 \times (\vA{80}/\vB{180})^2 = \vD{62.7} \text{ kg}$
3. Hume: $0.3281 \times \vA{80} + 0.33929 \times \vB{180} - 29.5336 = \vE{57.8} \text{ kg}$
4. Average: $(\vC{61.4} + \vD{62.7} + \vE{57.8}) \div 3 = 60.6 \text{ kg}$ — about 75.8% of total body weight.