Lean Body Mass Calculator
Lean body mass is everything you weigh except fat. Estimate it from your height and weight with four published formulas, or enter your body fat % for a number based on your own body.
Your details
Your results
Enter your sex, weight and height to estimate your lean body mass.
Lean body mass
- Lean share of weight
- %
- Fat mass
| Equation | Lean mass |
|---|---|
| Boer (1984) | |
| Janmahasatian (2005) | |
| Hume (1966) | |
| James (1976) |
How to use it
- Choose your units, then enter your sex, weight and height.
- If you know your body fat %, add it. The main result then uses your weight minus your fat.
- Without a body fat %, the main result uses the Boer formula. The table compares four formulas.
How it's calculated
From your body fat %. Lean mass = weight × (1 − body fat % ÷ 100). This is the main result when you enter a body fat %.
From height and weight. W is weight in kg, H height in cm.
| Formula | Men | Women |
|---|---|---|
| Boer (1984) | 0.407 × W + 0.267 × H − 19.2 | 0.252 × W + 0.473 × H − 48.3 |
| Janmahasatian (2005) | 9,270 × W ÷ (6,680 + 216 × BMI) | 9,270 × W ÷ (8,780 + 244 × BMI) |
| Hume (1966) | 0.32810 × W + 0.33929 × H − 29.5336 | 0.29569 × W + 0.41813 × H − 43.2933 |
| James (1976) | 1.1 × W − 128 × (W ÷ H)² | 1.07 × W − 148 × (W ÷ H)² |
Without a body fat %, the main result uses Boer; the summary shows the range across the formulas. Pounds, feet and inches are converted first.
Limits. These formulas predict the average lean mass for people of your height and weight. They can’t see how much of your weight is muscle. Most were built for dosing medicines, where an average estimate is good enough. From a BMI of 35, the James formula is left out because it stops making sense.
Sources
- Boer, P. (1984). Estimated lean body mass as an index for normalization of body fluid volumes in humans. American Journal of Physiology, 247(4), F632–F636.
- Janmahasatian, S., Duffull, S. B., Ash, S., Ward, L. C., Byrne, N. M., & Green, B. (2005). Quantification of lean bodyweight. Clinical Pharmacokinetics, 44(10), 1051–1065.
- Hume, R. (1966). Prediction of lean body mass from height and weight. Journal of Clinical Pathology, 19(4), 389–391.
- James, W. P. T. (1976). Research on Obesity: a report of the DHSS/MRC group. London: HMSO.
Questions
What is lean body mass?
Your total weight minus your body fat. It includes muscle, bone, organs, skin and water. Muscle is only part of it, so a change in lean mass isn't the same as a change in muscle.
Which formula should I trust?
If you have a decent body fat estimate, use that. Otherwise the formulas give a range. They were built on average adults, so they tend to underestimate lean mass in muscular people and overestimate it in people with more body fat.
Why is the James formula sometimes not shown?
At high BMI, the James formula breaks down and can even predict less lean mass as weight goes up. The calculator leaves it out from a BMI of 35.
What do I use lean body mass for?
Some protein targets and the Katch-McArdle BMR equation are based on lean mass, and it's the input for the Fat-Free Mass Index. It's also a better way than weight alone to see whether a diet is costing you muscle.
Updated November 9, 2026.