Weight & Body tool
Lean Body Mass Calculator
Estimate your lean body mass from height, weight and sex with the Boer, James and Hume formulas, plus an estimated body fat share. Metric or imperial. Free.
Nothing you enter leaves your device.
Inputs
Results
Enter values to see your results.
Simple steps
How it works
- 01
Choose units and your sex.
- 02
Enter your height and weight.
- 03
Select Calculate to compare the three formulas and their average.
Good to know
Frequently asked questions
What is lean body mass?
Everything in your body except fat: muscle, bone, organs, skin and water. It is often used to plan protein intake or estimate calorie needs.
Which formula is best?
The Boer formula is the most widely used for adults. James and Hume give slightly different results, so the calculator shows all three and their average.
Why is the body fat figure only an estimate?
It is your weight minus the average lean mass. A tape-measure or scan method is more accurate; try our body fat calculator.
Is it accurate for athletes?
Less so. The formulas use height and weight only, so they tend to underestimate lean mass in very muscular people.
Can I use pounds and inches?
Yes. Choose imperial units; results are shown in pounds.
Is anything I enter stored or sent?
No. The calculation runs in your browser. Nothing you type is saved or sent to a server.
How it is calculated
Boer (1984): men 0.407 × weight + 0.267 × height − 19.2; women 0.252 × weight + 0.473 × height − 48.3. James (1976): men 1.1 × weight − 128 × (weight ÷ height)²; women 1.07 × weight − 148 × (weight ÷ height)². Hume (1966): men 0.32810 × weight + 0.33929 × height − 29.5336; women 0.29569 × weight + 0.41813 × height − 43.2933. Weight in kg, height in cm.
Sources
- Boer P. Estimated lean body mass as an index for normalization of body fluid volumes in humans. Am J Physiol 1984;247:F632–6
- James WPT. Research on obesity. London: HMSO, 1976
- Hume R. Prediction of lean body mass from height and weight. J Clin Pathol 1966;19:389–91
Last reviewed: October 14, 2026