The formulas
W is weight in kilograms and H is height in centimeters. The result is lean body mass in kilograms.
| Formula | Men | Women |
|---|---|---|
| Boer (1984) | 0.407 W + 0.267 H − 19.2 | 0.252 W + 0.473 H − 48.3 |
| James (1976) | 1.1 W − 128 (W ÷ H)² | 1.07 W − 148 (W ÷ H)² |
| Hume (1966) | 0.32810 W + 0.33929 H − 29.5336 | 0.29569 W + 0.41813 H − 43.2933 |
Implied body fat % = (weight − lean body mass) ÷ weight × 100
Worked example
A man who is 180 cm tall and weighs 80 kg:
Boer: 0.407 × 80 + 0.267 × 180 − 19.2 = 32.56 + 48.06 − 19.2 = 61.4 kg
James: 1.1 × 80 − 128 × (80 ÷ 180)² = 88 − 25.28 = 62.7 kg
Hume: 0.32810 × 80 + 0.33929 × 180 − 29.5336 = 57.8 kg
James: 1.1 × 80 − 128 × (80 ÷ 180)² = 88 − 25.28 = 62.7 kg
Hume: 0.32810 × 80 + 0.33929 × 180 − 29.5336 = 57.8 kg
So about 58 to 63 kg of his 80 kg is lean mass, which implies roughly 22% to 28% body fat.
Limitations
- These formulas only use height, weight and sex. They can't see muscle, so they're often off for athletes.
- The James formula breaks down at higher weights: past a certain point it predicts lean mass going down as weight goes up. Calcist flags it as not reliable from a BMI of 35, and when it stops making sense.
- They were developed on adults, largely for drug dosing and fluid calculations.
- If you know your body fat percentage from a tape measurement or scan, lean mass = weight × (1 − body fat %) is more direct.
- These are adult formulas, for people 18 and over. Children and teens are still growing, and the CDC uses growth charts for them.
Sources
- Boer P. Estimated lean body mass as an index for normalization of body fluid volumes in humans. Am J Physiol 1984;247:F632–F636.
- James WPT. Research on Obesity: a report of the DHSS/MRC group. HMSO, London; 1976.
- Hume R. Prediction of lean body mass from height and weight. J Clin Pathol 1966;19:389–391.
- Janmahasatian S, et al. Quantification of lean bodyweight. Clin Pharmacokinet 2005;44:1051–1065. — explains why the James formula fails at high weights.