Lean Body Mass Calculator
Find your lean mass and lean percentage
Free Lean Body Mass Calculator
Boer, James and Hume formulas, or your own body fat percentage
Lean body mass is everything in your body that is not fat: muscle, bone, organs and water. This calculator estimates it from height, weight and gender with three validated formulas (Boer, James and Hume) and, if you know your body fat percentage, gives the exact figure as weight × (1 − body fat). The Boer formula is shown as the main result because it is the most widely used. Lean mass is the basis for protein targets, some medication doses and for tracking whether weight changes come from muscle or fat.
Features
3 formulas
Boer, James and Hume side by side
Exact with body fat
Enter your body fat % for a direct calculation
Metric and imperial
cm/kg or in/lb
Private
Your measurements never leave your device
Formulas
Boer (1984)
- Men: 0.407 × weight + 0.267 × height − 19.2
- Women: 0.252 × weight + 0.473 × height − 48.3
- Weight in kg, height in cm
James and Hume
- James men: 1.1 × weight − 128 × (weight/height)²
- James women: 1.07 × weight − 148 × (weight/height)²
- Hume men: 0.3281 × weight + 0.3393 × height − 29.53
- Hume women: 0.2957 × weight + 0.4181 × height − 43.29
Frequently Asked Questions
How is lean body mass calculated?
The most accurate way is from body fat: lean mass = weight × (1 − body fat %). Without a body fat figure, the Boer, James and Hume formulas estimate it from height and weight.
Is lean body mass the same as muscle mass?
No. Lean mass includes muscle, bone, organs, water and connective tissue; skeletal muscle is roughly half of it. Lean mass is still a practical way to track muscle gain.
What is a normal lean percentage?
Typically 75–90% for men and 65–85% for women, with athletes near the top of the range. It equals 100 minus body fat percentage.
Which formula is most accurate?
Boer is the most consistent across the general population and is used in clinical settings; James can drift for people with obesity. The average of the three is also a sound estimate.
How do I increase lean mass?
Resistance training, 1.6–2.2 g of protein per kg of body weight and a modest calorie surplus. Use the FFMI calculator to track muscularity relative to height.