Free lean body mass calculator estimates lean mass and body fat percentage from height and weight using the Boer and James formulas for men and women.
Lean body mass (LBM) is everything in your body except fat: muscle, bones, organs, skin and water. It is a better guide to body composition than body weight alone, because two people of the same weight can have very different fat and muscle proportions.
This calculator estimates your LBM from height, weight and sex using two validated predictive equations. The Boer formula is the default and is widely used in clinical research; the James formula gives a slightly different estimate and is useful as a cross-check.
The results show your estimated lean mass, fat mass in kilograms and body fat percentage. Use them to track changes over time: if your weight stays the same but your body fat percentage drops, you are gaining lean mass.
Enter your details and choose a formula - the estimate updates instantly.
Lean body mass is your total body weight minus fat mass: muscle, bones, organs, skin and water. It is often used as a proxy for muscle mass, although the two are not identical.
Both are validated equations used in clinical settings. Boer is more common in research and is the default here. Neither is exact: for most people they differ by 1-3 kg, and both can differ from a DEXA scan by several percent.
Men typically have a higher proportion of muscle and lower essential fat, so the equations use separate coefficients for men and women. Entering the wrong sex can shift the result by several kilograms.
Yes. Progressive strength training plus enough protein (about 1.6-2.0 g per kg) builds lean mass, especially in combination with a small calorie surplus. Changes are slow, so track trends over months.
No. LBM includes bones, organs, skin and water in addition to muscle. Skeletal muscle is typically about half of total LBM, so the two numbers should not be used interchangeably.
DEXA is the reference method. Bioimpedance scales, skinfold calipers and tape-measure formulas are convenient but less precise. Whatever method you choose, use the same one consistently to compare results.