Lean Body Mass Calculator
Estimate lean body mass and body-fat weight (Boer formula).
Input sheet
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Lean body mass is everything you weigh that isn't fat — muscle, bone, organs, and water. Knowing it helps you set protein targets, judge whether weight changes are muscle or fat, and track progress better than the scale alone.
How it works
The Boer formula estimates lean body mass from height and weight, with sex-specific coefficients. Body-fat weight is total weight minus lean mass.
This calculator uses the Boer formula, which estimates lean mass from height and weight with sex-specific coefficients. It works in metric internally (converting your pounds and feet/inches), then converts the result back to pounds.
Because it's height-and-weight based, it's an estimate rather than a measurement. Two people at the same height and weight get the same answer even if their actual muscularity differs, so treat it as a useful baseline rather than a precise body-composition reading.
Men: lean mass (kg) = 0.407 × weight(kg) + 0.267 × height(cm) − 19.2. Women: lean mass (kg) = 0.252 × weight(kg) + 0.473 × height(cm) − 48.3. Body-fat weight = total weight − lean mass.
Worked examples
A man at 5'10" (178 cm) weighing 175 lb (79.4 kg). → About 133.6 lb lean mass and 41.4 lb of fat (76% lean).
0.407 × 79.4 + 0.267 × 177.8 − 19.2 ≈ 60.6 kg → 133.6 lb; 175 − 133.6 = 41.4 lb fat.
A woman at 5'6" (168 cm) weighing 150 lb (68.0 kg). → About 106 lb lean mass and 44 lb of fat.
0.252 × 68.0 + 0.473 × 167.6 − 48.3 ≈ 48.1 kg → about 106 lb.
Tips & gotchas
- Use lean mass, not total weight, to set protein targets — muscle is what drives the requirement.
- During a cut, watch that lean mass holds steady; a drop means you're losing muscle and should add protein or ease the deficit.
- Pair this estimate with a tape measure or progress photos, since the scale alone can't tell muscle gain from fat gain.
- For a true reading, a DEXA scan or hydrostatic test beats any height-weight formula.
FAQ
How is lean body mass different from muscle mass?
Lean mass includes muscle plus bone, organs, and water. Skeletal muscle is only part of it, so your lean-mass number will always be larger than your muscle weight alone.
Why might this estimate be off for me?
Formulas based on height and weight can't see your actual build. A very muscular or very lean person at a given height and weight will read differently than the average the formula assumes.
Should lean mass stay flat while losing fat?
Ideally yes. Holding lean mass roughly steady while total weight drops is the sign of a well-run cut with enough protein and resistance training.
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