Lean Body Mass Calculator

What lean body mass means

Lean body mass (LBM) is everything in your body that isn't fat: muscle, bone, organs, connective tissue and water. It's used to set protein targets more precisely than bodyweight alone, to estimate resting metabolic rate with formulas like Katch-McArdle, and to track body-composition changes over time in a way that total weight can't — you can lose fat and gain muscle simultaneously with the scale barely moving, and LBM tracking is one way to see that happening.

The three formulas

This calculator estimates LBM from height, weight and sex alone — no tape measure needed — using one of three published regression formulas, toggled in one tool:

• Boer (1984) is the most commonly cited general-population formula and the default here.
• James (1976) weights the height-to-weight relationship differently and can diverge more for people outside average height and weight ranges.
• Hume (1966) is the oldest of the three, still referenced in some clinical drug-dosing contexts.

Each uses sex-specific coefficients because fat distribution and frame composition differ systematically between men and women in the populations these formulas were derived from.

Why the results differ from each other

Every formula here is a population-average regression, fit to a specific historical sample using only height, weight and sex — none of them measures your actual body composition. Differences of one to three kilograms between formulas for the same person are normal and expected; they reflect different underlying assumptions, not one formula being more "correct." If you want a direct measurement instead of a height/weight estimate, the body fat calculator (US Navy circumference method) elsewhere in this hub uses actual tape measurements and will usually be more personalized.

How to use the result

The tool also reports estimated fat mass and fat percentage, calculated simply as the difference between your total weight and the estimated lean mass. Use LBM as an input to other calculations — for example, protein intake is sometimes set per kilogram of lean mass rather than total weight for people carrying significant body fat, since muscle tissue is what actually uses the protein. Track the trend over time with a consistent formula rather than switching formulas between measurements, since switching alone can look like a body-composition change that isn't real.

Limits

These are height/weight regression estimates, not measurements — they can't see your actual muscle mass, and will be less accurate for people who are unusually muscular, unusually lean, or otherwise outside the populations the formulas were built from. For a more personalized estimate, pair this with the body fat calculator's circumference-based method. This tool is informational and not medical advice.