Lean Body Mass Calculator
Enter your weight and, if you know it, your body fat percentage. We work out how much of your weight is lean mass.
This calculator gives general estimates for information only. It is not medical advice and does not replace a consultation with a doctor or other qualified health professional.
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The formula
Lean mass = weight x (1 - body fat %). Boer formula (men): 0.407 x kg + 0.267 x cm - 19.2. Women: 0.252 x kg + 0.473 x cm - 48.3.
What lean body mass is
It is everything in your body that is not fat: muscle, bone, organs, skin and water. It matters because muscle drives your metabolism, strength and long-term health.
Two ways to find it
If you know your body fat percentage, lean mass is simply your weight minus the fat. For a 75 kg person at 20 percent body fat, fat mass is 15 kg and lean mass is 60 kg.
If you do not, we estimate it with the Boer formula, which uses sex, height and weight. It is a reasonable guess but less accurate than a measured body fat figure.
Using it
Lean mass is the basis of the Katch-McArdle BMR formula and is useful for setting protein targets. Tracking it over time tells you whether a weight change is fat, muscle or both.
Examples to check
Type these into the calculator above to see how it behaves. Every result below was produced by the same calculator code that runs on this page.
| What you enter | What you get |
|---|---|
| Male; Height (cm): 180; Weight (kg): 80; Body fat % (optional): 18 | Lean body mass: 65.6 kg |
| Female; Height (cm): 165; Weight (kg): 62; Body fat % (optional): 26 | Lean body mass: 45.9 kg |
| Male; Height (cm): 175; Weight (kg): 75 | Lean body mass: 58.1 kg |
Lean Body Mass Calculator: frequently asked questions
How can I increase lean mass?
Strength training two to three times a week, enough protein, enough total calories and good sleep.
Can I rely on this result as medical advice?
No. It is a general estimate for information only. It cannot replace a check-up, and your doctor can interpret the numbers for your own situation.
Is what I enter in this calculator saved or sent anywhere?
No. The calculation runs in your browser, so what you enter is not sent to our servers. We only count, anonymously, whether a tool ran successfully.
Is this calculator free to use?
Yes. It is free, needs no sign-up and has no usage limit.
Last reviewed: October 3, 2026