Lean Body Mass Calculator
Your fat-free mass from height and weight
Lean Body Mass
- 1Choose your sexThe formulas differ for men and women
- 2Enter weight and heightIn kg or lb, cm or ft + in
- 3See your lean massThree formulas compared
Lean body mass formulas
Lean body mass is your weight minus your body fat: muscles, bones, organs, skin and water. These formulas use weight (kg) and height (cm):
Boer, men: 0.407W + 0.267H − 19.2
Boer, women: 0.252W + 0.473H − 48.3
James, men: 1.1W − 128(W/H)²
Hume, men: 0.32810W + 0.33929H − 29.5336
Why lean mass matters
Lean mass drives your resting metabolism, so it's used in the Katch–McArdle BMR formula and for dosing some medicines. Keeping it up while losing weight means losing fat rather than muscle.
Getting a more accurate number
Formulas assume an average build. If you know your body fat percentage from a tape measurement or scan, lean mass = weight × (1 − body fat %).
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Frequently asked questions
What is a normal lean body mass?
Typically about 70–90% of body weight for men and 60–80% for women, depending on fitness.
Is lean body mass the same as muscle mass?
No. Lean mass includes muscle plus bones, organs, skin and water. Muscle is roughly half of it.
How can I increase my lean body mass?
Strength training two to four times a week and enough protein (about 1.6 g per kg of body weight) are the most effective ways.
Sources
- Boer P. Estimated lean body mass as an index for normalization of body fluid volumes, 1984
Last reviewed: October 2026