Lean Body Mass Calculator
Estimate your lean body mass, the weight of everything except fat.
Runs in your browser — nothing is sent or saved.
How to work out lean body mass
- Choose your sex.
- Pick metric or imperial, then enter your height and weight.
- Read your lean body mass by three formulas.
- Copy the link to save or share the result.
What lean body mass means
Lean body mass, also called fat-free mass, is the weight of everything in your body except fat: muscle, bone, organs, and water. This LBM calculator estimates it for you. It is the mirror image of fat mass, and the two add up to your total weight. Knowing it is useful for dosing some medicines, setting protein targets, and tracking whether weight you lose is fat rather than muscle.
The three formulas
Each estimates lean mass from sex, height, and weight, and they agree closely for most people.
| Formula | Year |
|---|---|
| Boer | 1984 |
| James | 1976 |
| Hume | 1966 |
Sources: Boer P (1984); James W (1976); Hume R (1966). The Boer formula for a man is 0.407 times weight in kg, plus 0.267 times height in cm, minus 19.2; for a woman the constants change.
The more accurate way: use body fat
Because these formulas use only height and weight, they cannot see your actual muscle, so a very muscular or very lean person is estimated less well. The direct route is to measure body fat first: lean body mass equals your weight times one minus your body-fat percentage. If you have a body-fat estimate, that figure is more personal than any height-and-weight formula.
An estimate, not medical advice
Treat these numbers as a guide, not a measurement. A body scan such as DEXA is the accurate option. Use this to track change over time, and see a doctor or dietitian for health decisions.
FAQ
How to calculate lean body mass?
If you want to know how to calculate lean body mass, enter your sex, height, and weight, and the tool applies the Boer, James, and Hume formulas. If you know your body-fat percentage, a more direct estimate is weight times one minus that percentage.
What is a normal lean body mass?
It varies with size and sex, but lean mass is often around 60 to 90% of total weight, higher in men and in leaner or more muscular people. There is no single normal figure.
What is the difference between lean body mass and muscle?
Lean body mass includes muscle plus bone, organs, and water, so it is larger than muscle mass alone. Muscle is one part of it.
Which lean body mass formula is best?
They give similar results for most people. Boer is a common default. For a lean or very muscular build, using a measured body-fat percentage is more reliable than any of them.
Are my details private?
Yes. The calculation runs in your browser and nothing you enter is uploaded or saved.