Know your body
Lean body mass calculator
Lean body mass is everything that is not fat: muscle, bone, organs and water. If you know your body-fat percentage, it is simple arithmetic. If you do not, population equations give a starting estimate.
Your numbers
Leave blank to use the population equations.
Your lean mass appears here
Enter height and weight. Add body fat for a far more individual answer.
How it’s calculated
With a body-fat estimate
Lean mass = weight × (1 − body fat %). This is the most accurate option available here, and the one we use when you provide body fat.
Without one
- Boer (1984): men 0.407W + 0.267H − 19.2; women 0.252W + 0.473H − 48.3.
- James (1976): men 1.1W − 128(W/H)²; women 1.07W − 148(W/H)².
- Hume (1966): men 0.32810W + 0.33929H − 29.5336; women 0.29569W + 0.41813H − 43.2933. (W in kg, H in cm.) Boer is usually the least biased in adults of normal build, so it is shown as the headline.
Limitations
The equations assume average muscularity for your height and weight. They underestimate lean mass in trained lifters and overestimate it in people with obesity.
Full sources and limitations are on the methodology page. Estimates are for healthy adults and are not medical advice.
Questions
What is the difference between lean body mass and fat-free mass?
In practice they are used interchangeably. Strictly, lean body mass includes a small amount of essential fat; fat-free mass includes none.
Which formula should I trust?
None of them, if you lift. Get a body-fat estimate — even a tape-measure one — and the calculation becomes far more individual.