Lean Body Mass Calculator

Lean body mass, also called fat-free mass, is your total body weight minus your fat mass. It includes muscle, bone, organs, connective tissue, and body water. This calculator estimates it rather than measuring it directly.

The calculator uses established estimation formulas. The Boer formula and the Hume formula derive fat-free mass from your height, weight, and sex. The underlying principle is: lean body mass = total weight − fat mass. Because the formulas are based on population data, they give an approximation for the relevant group.

Each formula was developed from a different sample and weights height and weight slightly differently, so their results can vary a little. Comparing several formulas gives you a plausible range rather than a single value.

It is an estimate based on body measurements, not a direct measurement. More precise methods such as DEXA, hydrostatic weighing, or bioelectrical impedance measure body composition directly. For very muscular or very underweight individuals, formula-based values can deviate more.

Fat-free mass is used, among other things, to estimate resting metabolic rate, track training progress, or plan nutrition goals. It complements BMI, which does not distinguish between muscle and fat.

No. The values are for general information and orientation. For an accurate measurement of body composition or any health concerns, consult a physician.