Lean Body Mass Calculator

Your lean body mass (LBM) is everything in your body that is not fat — muscle, bone, organs, connective tissue, and water. Knowing it helps you set protein targets, gauge muscle gain, and dose certain medications. This calculator uses the Boer formula as its primary estimate and shows the Hume formula alongside it for comparison.

The Formulas

Both formulas predict LBM in kilograms from weight (kg) and height (cm), with separate coefficients for each sex.

Fat mass is then simply total weight − LBM.

Worked Example

An 80 kg man, 180 cm tall, using the Boer formula:

• LBM = 0.407 × 80 + 0.267 × 180 − 19.2
• = 32.56 + 48.06 − 19.2 = 61.4 kg lean mass
• Fat mass = 80 − 61.4 = 18.6 kg

Typical Lean-Mass Share

Why Two Formulas?

Boer and Hume were derived from different populations and tend to agree within 1-2 kg for most people. Seeing both gives you a sense of the estimate's uncertainty — if they diverge sharply, your build may sit outside the formulas' typical range and a direct measurement is worth considering.

Using LBM in Practice

A common protein target for active people is 1.6-2.2 g per kg of lean mass. LBM is also the basis of the Katch-McArdle BMR equation, making it a useful input for nutrition planning.

Note: These are estimation formulas based on height, weight, and sex — they do not measure body fat directly and may differ from DEXA or hydrostatic results. Use them as a guide, not a clinical figure.