Your lean body mass is your weight minus your fat. Estimate it from height and weight, or exactly from a body fat reading.
Lean body mass
134.2lb
Boer formula
Body fat (implied)
23.9%
| Formula | Lean mass | Fat implied |
|---|---|---|
| Boer (1984) | 134.2 lb | 23.9% |
| James (1976) | 137.0 lb | 22.3% |
| Hume (1966) | 125.9 lb | 28.6% |
| Formula | Men | Women |
|---|---|---|
| Boer | 0.407W + 0.267H − 19.2 | 0.252W + 0.473H − 48.3 |
| James | 1.1W − 128(W/H)² | 1.07W − 148(W/H)² |
| Hume | 0.32810W + 0.33929H − 29.5336 | 0.29569W + 0.41813H − 43.2933 |
W = weight in kg, H = height in cm.
These equations were built from average populations, so they assume average muscularity. A lifter with more muscle than average will have more lean mass than they predict; entering a body fat percentage fixes that.
Everything you weigh that is not fat: muscle, bone, organs, skin, water and connective tissue. Muscle is only part of it, typically 40–50% of lean mass.
If you know your body fat percentage, calculating from it is the most direct. Without it, the Boer formula is generally considered the best of the height-and-weight equations for adults, though none account for how muscular you are.
It drives your resting metabolism (the Katch-McArdle formula uses it), sets sensible protein targets, and is used for some medication dosing. Tracking it shows whether weight you lose is fat or muscle.