Lean Body Mass (LBM) Calculator
What is my lean body mass?
Result
How it is calculated
Lean body mass (LBM) is your weight minus fat. The tool uses a Boer-style regression with height in cm and weight in kg. For men: LBM = 0.407 × weight + 0.267 × height − 19.2. For women: LBM = 0.252 × weight + 0.473 × height − 48.3. Fat mass is then weight − LBM, never below zero. Both results are in kg with two decimals. This is a population-level estimate from formulas, not a body scan, so it can be off for very muscular or very lean people, children and older adults.
Worked example
A man of 175 cm and 70 kg. Weight term: 0.407 × 70 = 28.49. Height term: 0.267 × 175 = 46.725. LBM = 28.49 + 46.725 − 19.2 = 56.015, shown as 56.02 kg. Fat mass is 70 − 56.015 = 13.985, shown as 13.99 kg. That is a body fat share of roughly 20% (13.985 / 70).
Common mistakes
- Entering height in metres or inches and weight in pounds; the formulas expect centimetres and kilograms.
- Selecting the wrong sex, which changes the coefficients and moves the result by several kilograms.
- Reading the fat mass figure as an exact body-fat measurement; it is an estimate derived from the formula.
- Confusing lean mass with muscle mass: lean mass also includes bone, organs and water.
About this calculator
This calculator estimates lean body mass — your total body weight minus body fat, covering muscle, bone, organs and water — from your sex, height and total weight, using the Boer formula, one of the standard equations developed to estimate this figure without specialized scanning equipment. Subtracting the result from total body weight also yields an estimated fat mass.
Lean body mass is a more meaningful number than total weight alone for people tracking fitness progress, since it distinguishes muscle gain from fat loss when weight on the scale barely moves during a training program. It is also used clinically to guide medication dosing and nutritional needs, since some drug dosages and calorie or protein targets are calculated relative to lean mass rather than total body weight, particularly for people with a higher body fat percentage where total-weight-based estimates would be inaccurate.
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