Estimate your lean body mass in kilograms and pounds from your sex, height and weight, or from a known body-fat percentage, and see how your weight splits into lean mass and fat mass.
The bar shows how your total body weight divides into lean mass and fat mass. The width of each part follows the numbers above.
| Formula | Lean body mass | Fat mass | In plain words |
|---|
The headline result uses the Boer formula, the most widely used estimate. Boer, Hume and James weight height and weight differently, so they rarely agree exactly. In body-fat mode all three rows show the direct result from your entered body-fat percentage.
For beginners: how to read this result
To get a result, pick a preset or enter your own body. Choose your sex, switch between metric (kg and cm) and imperial (lb and in), then select how you want lean mass estimated: from your height and weight, or from a body-fat percentage you have already measured.
What lean body mass is
Lean body mass, often shortened to LBM, is everything in your body that is not fat: muscle, bone, organs, connective tissue and the water they hold. It is closely related to muscle but not the same thing. Fat mass is the rest of your weight, so lean mass and fat mass always add up to your total body weight.
How the formulas work
With weight W in kilograms and height H in centimetres, the calculator uses three established estimates:
- Boer (the headline result): men use 0.407 multiplied by W plus 0.267 multiplied by H minus 19.2; women use 0.252 multiplied by W plus 0.473 multiplied by H minus 48.3.
- Hume: men use 0.32810 multiplied by W plus 0.33929 multiplied by H minus 29.5336; women use 0.29569 multiplied by W plus 0.41813 multiplied by H minus 43.2933.
- James: men use 1.1 multiplied by W minus 128 multiplied by the square of W divided by H; women use 1.07 multiplied by W minus 148 multiplied by the square of W divided by H.
The three formulas weight height and weight differently, so they rarely agree exactly. The comparison table shows all three side by side, with the Boer result highlighted as the headline figure.
Estimating from a known body-fat percentage
If you have a measured body-fat percentage from calipers, a body scan or a smart scale, the body-fat mode is more accurate than the height and weight formulas. It uses a direct relationship: lean body mass equals weight multiplied by one minus the body-fat fraction. Fat mass is then your weight minus that lean mass.
Mass, not percentage
This calculator answers in kilograms and pounds. A body-fat percentage calculator answers the same question as a percentage. Both describe the same body, just from different angles, and the lean versus fat split bar makes the relationship easy to see at a glance.
What is not included
These figures are estimates from population formulas, not a direct measurement of your body composition. They do not account for your individual frame, muscle distribution, hydration, age or health conditions, and a body scan or hydrostatic weighing gives a more precise result. This is general information, not medical advice.