The lean body mass formulas
Lean body mass is total weight minus fat. Several validated equations estimate it from height and weight by sex. All use weight in kilograms and height in centimetres:
Boer (men) = 0.407·W + 0.267·H − 19.2
Boer (women) = 0.252·W + 0.473·H − 48.3
James (men) = 1.1·W − 128·(W/H)²
Hume (men) = 0.32810·W + 0.33929·H − 29.5336
where W is weight in kg and H is height in cm. The calculator converts US units for you and reports all three.
Worked example
For a man who is 178 cm and 80 kg, the Boer formula gives:
Boer: 0.407 × 80 + 0.267 × 178 − 19.2 = 32.56 + 47.53 − 19.2 = 60.9 kg of lean mass.
Implied fat mass: 80 − 60.9 = 19.1 kg (about 24% body fat).
Why lean body mass matters
| Use | Why LBM helps |
|---|---|
| Protein targets | Many guidelines set protein per kg of lean mass, not total weight. |
| Fat-loss tracking | Shows whether lost weight is fat or muscle. |
| Medication dosing | Some drug doses are based on fat-free mass. |
| Fitness goals | Preserving lean mass while cutting is a common aim. |
Heads up: these equations are population estimates and can be inaccurate for very muscular or very lean people. For precise body composition, a DEXA scan or hydrostatic weighing is the reference standard. The formulas here come from peer-reviewed clinical research, including published validation studies on LBM equations.