Lean Body Mass Calculator
Work out how much of your weight is muscle, bone, organs and water using the Boer, James and Hume equations — or directly from your body fat percentage.
Your details
Formula comparison
| Formula | Lean body mass |
|---|
Body composition split
The three LBM equations
James — men: 1.1W − 128(W/H)² · women: 1.07W − 148(W/H)²
Hume — men: 0.32810W + 0.33929H − 29.5336 · women: 0.29569W + 0.41813H − 43.2933
W = weight in kg, H = height in cm
If body fat % is known: LBM = W × (1 − body fat % / 100)
Lean body mass is everything that is not fat: muscle, bone, organs, skin and body water. It is the part of your weight that drives strength, resting metabolism and how much protein you need. Because it correlates with drug clearance, it is also used clinically to dose anaesthetics and chemotherapy.
Which number to trust
If you have a reliable body fat percentage, use that route — it is the most direct. Otherwise Boer is the usual default and tends to agree best with reference methods across normal body sizes. James loses accuracy at the extremes of weight, and Hume sits between the two. If you are tracking a training phase, the trend across months matters more than which equation you picked.
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