Estimate your lean body mass (LBM) — your total weight minus body fat — using three established formulas: Boer, James, and Hume.
LBM = total body weight minus fat mass. It includes muscle, bone, water, and organs.
| Formula | Description |
|---|---|
| Boer | Most widely cited formula for clinical use |
| James | Derived from a large population study |
| Hume | Based on body density measurements |
| Formula | LBM (kg) | LBM (lb) | % of body |
|---|---|---|---|
| Boer | 56 | 123.5 | 80% |
| James | 56.5 | 124.6 | 80.7% |
| Hume | 52.8 | 116.4 | 75.4% |
| Average | 55.1 | 121.5 | 78.7% |
These formulas use height and weight only. For a more accurate measurement of body composition, consider DEXA scanning or hydrostatic weighing.
The oldest of the three equations behind this page comes from a 1966 paper by R. Hume in the Journal of Clinical Pathology, titled 'Prediction of lean body mass from height and weight'. Boer's version followed in 1984, and the James equation completes the set. All three guess your lean mass, meaning weight minus fat (muscle, bone, organs and body water), from height, weight and sex alone. This calculator runs all three, averages them and shows the fat mass left over.
With weight W in kilograms and height H in centimeters. Boer: men 0.407 W + 0.267 H − 19.2; women 0.252 W + 0.473 H − 48.3. James: men 1.10 W − 128 (W/H)²; women 1.07 W − 148 (W/H)². Hume: men 0.3281 W + 0.3393 H − 29.5336; women 0.2969 W + 0.4165 H − 43.2933. In US mode pounds are multiplied by 0.453592 and inches by 2.54 first.
Worked example: a woman 165 cm tall weighing 60 kg. Boer = 0.252 × 60 + 0.473 × 165 − 48.3 = 15.12 + 78.045 − 48.3 = 44.9 kg. James = 1.07 × 60 − 148 × (60/165)² = 64.2 − 19.57 = 44.6 kg. Hume = 17.814 + 68.723 − 43.293 = 43.2 kg. The average is 44.2 kg (97.5 lb), or 73.7 percent of body weight, which leaves 15.8 kg of fat mass. The page shows that fat share as a whole number, 26 percent.
What the page does not know. Height and weight are the only inputs, so two people with identical numbers but different muscle can have very different true lean mass, and age, training and frame size play no part. The formulas also drift apart in larger bodies: at 175 cm and 150 kg, a man gets 88.6, 71.0 and 79.1 kg from the three, and the James equation in particular curves downward at high weights. The page's female Hume coefficients are rounded slightly differently from the published 0.29569 and 0.41813, worth about 0.2 kg in the example above. The American Council on Exercise publishes body fat categories for athletes, fitness and the general population if you want context for a percentage, but this is an estimate for general education and not medical advice.
They were fitted to different groups and use different shapes of equation. Near average builds they usually land within a few kilograms of each other, and the gap widens at the extremes, so the spread itself tells you how uncertain the estimate is.
No. Lean mass includes muscle but also bone, organs, connective tissue and body water, so it is always larger than muscle alone.
Treat it as a rough inference, not a measurement. It is just weight minus a height-and-weight estimate. For an actual reading, ask about skinfold, bioimpedance or DEXA, and discuss any health decisions with a clinician.
Because the equations assume typical proportions. Someone far more muscular than average will have more lean mass than any of the three predict, and the fat mass shown will be overstated.