Lean Body Mass Calculator
Estimate your lean body mass and fat mass using the Boer formula.
Results update as you type.
About this calculator
A lean body mass (LBM) calculator estimates the weight of everything in your body that is not fat — muscle, bone, organs and water — from your height, weight and sex. It uses the Boer formula by default, a well-validated prediction equation, with James and Hume as alternatives, and reports the remaining fat mass and body-fat percentage alongside it.
For a 175 cm, 75 kg man the Boer formula is 0.407 × 75 + 0.267 × 175 − 19.2 ≈ 58 kg of lean mass. Fat mass is then 75 − 58 = 17 kg, or about 23% body fat. Women use different constants (0.252 × weight + 0.473 × height − 48.3) because they carry proportionally more essential fat. The tool clamps results so lean mass never exceeds total weight.
Lean body mass is useful for setting protein and calorie targets, tracking whether a diet is costing you muscle, and, in medicine, for scaling some drug doses. Because these are prediction equations rather than a body scan, they are estimates — a DEXA scan or hydrostatic weighing is more precise for very lean or very heavy people. This is general information, not medical advice.
Frequently asked questions
What is the Boer formula?
For men, LBM = 0.407 × weight(kg) + 0.267 × height(cm) − 19.2; for women, LBM = 0.252 × weight + 0.473 × height − 48.3. It predicts lean mass from height and weight and is one of the most accurate simple equations.
Why does lean body mass matter?
It sets your resting metabolism and drug-dosing in medicine, and tracking it helps confirm you are losing fat rather than muscle. Protein and calorie targets are often based on LBM rather than total weight.
Is this the same as body-fat percentage?
They are two sides of the same number: fat mass is your weight minus lean body mass, and body-fat percentage is fat mass divided by total weight. The tool shows all three.
What is a normal lean body mass?
It scales with size and sex, but for a 175 cm, 75 kg man the Boer formula gives about 58 kg of lean mass and 17 kg of fat, roughly 23% body fat. Women carry more essential fat, so their lean percentage is lower at the same size.
Which lean-mass formula should I use?
Boer is the default and well validated for most adults; James and Hume are shown for comparison. They agree closely for average builds and diverge for very lean or very heavy people.
How do I increase lean body mass?
Resistance training with enough protein (often 1.6–2.2 g/kg) and adequate total calories builds muscle, the main component of lean mass. Tracking LBM during a diet helps confirm you are losing fat rather than muscle.
Is lean body mass the same as muscle mass?
No. Lean body mass includes muscle plus bone, organs, connective tissue and body water; skeletal muscle is only part of it. Muscle is the portion you can grow with training.
API — use this calculator from code
Call this calculator as a free JSON endpoint — no key required. Send the field values below as query parameters or JSON. Read the full API docs →
Endpoint
GET https://calculator.free/api/v1/lean-body-mass/curl
curl "https://calculator.free/api/v1/lean-body-mass/?sex=male&units=metric&height=175&weight=75"JavaScript fetch()
const r = await fetch(
"https://calculator.free/api/v1/lean-body-mass/?" + new URLSearchParams({
"sex": "male",
"units": "metric",
"height": "175",
"weight": "75"
}));
const data = await r.json();
console.log(data.results);Results are estimates for general guidance only, not financial, medical or tax advice.