How the Lean Body Mass Calculator Works
Lean body mass (LBM) is everything in your body except fat: muscle, bones, organs, skin and the water inside them. It is your total weight minus your fat mass. Knowing your LBM helps with fitness plans, medicine doses and calorie needs. The Lean Body Mass Calculator estimates it from your weight and height with well-known formulas.
What lean body mass includes
- Muscle: skeletal, smooth and heart muscle.
- Bones: the mineral mass of the skeleton.
- Organs and tissue: internal organs and connective tissue.
- Water: the water in your body and fluids.
- Essential fat: the small amount of fat that every cell needs. Only the extra, storage fat is left out.
What you enter
- Target group: Adult, or Child (14 years or younger).
- Biological gender: for adults, because the formulas differ for men and women.
- Unit system: Metric (kg and cm) or Imperial (lbs and inches). Switching converts what you typed.
- Body weight and height. For adults the weight must be about 30 to 300 kg and the height about 120 to 230 cm. For children, 3 to 80 kg and 45 to 190 cm.
The formulas
W is your weight in kilograms and H is your height in centimeters.
| Formula | Men | Women |
|---|---|---|
| Boer | 0.407 W + 0.267 H - 19.2 | 0.252 W + 0.473 H - 48.3 |
| James | 1.1 W - 128 (W/H)² | 1.07 W - 148 (W/H)² |
| Hume | 0.3281 W + 0.33929 H - 29.5336 | 0.29569 W + 0.41813 H - 43.2933 |
- Formula: Boer
Men: 0.407 W + 0.267 H - 19.2
Women: 0.252 W + 0.473 H - 48.3 - Formula: James
Men: 1.1 W - 128 (W/H)²
Women: 1.07 W - 148 (W/H)² - Formula: Hume
Men: 0.3281 W + 0.33929 H - 29.5336
Women: 0.29569 W + 0.41813 H - 43.2933
For adults the calculator shows all three and uses their average as the result. For children (the Peters formula) it first estimates the extracellular volume, and then multiplies:
eECV = 0.0215 x W^0.6469 x H^0.7236 LBM = 3.8 x eECV
A worked example
A man weighing 75 kg who is 178 cm tall (the default):
| Formula | Lean body mass |
|---|---|
| Boer | 58.9 kg |
| James | 59.8 kg |
| Hume | 55.5 kg |
| Average | 58.0 kg |
| Estimated fat mass (75 - 58.0) | 17.0 kg |
| Estimated body fat (17.0 / 75) | 22.6% |
More examples
| Person | LBM | Fat mass | Body fat |
|---|---|---|---|
| Woman, 60 kg, 165 cm | 44.3 kg | 15.7 kg | 26.1% |
| Child, 30 kg, 130 cm (Peters) | 25.0 kg | 5.0 kg | 16.8% |
Chart: the three formulas
For the 75 kg man, the three formulas give similar answers, and the average is used:
Boer ███████████████████████████████████████ 58.9 kg James ████████████████████████████████████████ 59.8 kg Hume █████████████████████████████████████ 55.5 kg Average ███████████████████████████████████████ 58.0 kg
Chart: lean mass and fat mass
The 75 kg man: the green part is lean mass, and the orange part is fat mass.
████████████████████████████████████████ lean 58.0 kg (77.4%) fat 17.0 kg (22.6%)
Good to know
- These are estimates from formulas, not measurements. A body scan (DEXA) or skinfold test is more reliable.
- If the formulas put your lean mass above your weight, no fat estimate is shown, because it would be negative.
- The Peters formula is for children of about 13 to 14 years old or younger.
- Muscle weighs more than fat for the same size, so LBM and body weight can move in different directions.
Tips
- Use the same scale and the same time of day when you track your weight.
- Compare your result with the Body Fat Calculator or the Army Body Fat Calculator, which use tape measurements.
This tool gives an estimate for general information only. It is not medical advice. Talk to a doctor before you change your diet or training.