Lean Body Mass Calculator
Find your lean body mass with the Boer formula from 1984, still the clinical standard. Use it to set protein against the tissue that uses it.
Members: the Phorme app recalculates this automatically as you log.
Everything that is not fat.
Lean body mass is your weight with the fat subtracted: skeletal muscle, bone, organs, skin, and water. It is the tissue that uses protein, moves the bar, and drives most of your resting energy burn, which makes it a better anchor than total body weight for several coaching decisions.
We estimate it with the Boer formula, published by P. Boer in 1984 from body composition data. It remains the default lean mass estimator in clinical drug dosing because it stays accurate across a wide range of body sizes while needing only sex, height, and weight.
Because the formula never sees your actual body fat, it assumes a typical composition for your height and weight. Very muscular and very lean people will read low; the implied body fat figure is the fastest way to sanity-check it against the tape-measure method.
- 1. Enter your sex, height, and weight.
- 2. Press Calculate to get your lean mass in pounds and kilos.
- 3. Check the implied body fat percent against the body fat calculator.
- 4. Carrying higher body fat? Set protein at 1 to 1.2 grams per pound of lean mass.
Men: LBM (kg) = 0.407 x weight (kg) + 0.267 x height (cm) minus 19.2 (Boer, 1984).
Women: LBM (kg) = 0.252 x weight (kg) + 0.473 x height (cm) minus 48.3 (Boer, 1984).
Questions we hear a lot.
What counts as lean body mass?
Everything except fat: skeletal muscle, bone, organs, skin, and body water. Muscle is usually a bit under half of the total, so LBM is not a muscle measurement, but at stable hydration a change in LBM mostly reflects muscle.
Why the Boer formula?
Boer published it in 1984 from body composition data, and it remains the default estimator in clinical drug dosing because it tracks measured lean mass well across a wide range of body sizes. It needs only sex, height, and weight.
When should I dose protein off lean mass instead of body weight?
At higher body fat levels. Per-pound-of-bodyweight targets overshoot for someone at 35 percent body fat, since fat tissue needs little protein. One to 1.2 grams per pound of lean mass gives a target that scales with the tissue protein actually maintains.
Can this tell me how much muscle I have gained?
Not directly. The formula estimates from height and weight, so it moves whenever weight moves, regardless of what the new weight is made of. Use it for a baseline, and track gain with strength numbers, circumference measurements, and photos.
Is lean body mass the same as fat-free mass?
Nearly. LBM includes the small amount of essential lipid in cell membranes and the nervous system; fat-free mass excludes all lipid. The difference is about 2 to 3 percent and does not change any training decision.
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