Lean body mass calculator
Estimate your lean body mass and fat mass with the Boer formula (weight, height, sex).
Boer formula (estimate). For accuracy, use bioimpedance or a specific test.
How the calculation works
Lean body mass (fat-free mass) is everything in the body that is not fat: muscle, bone, organs and water. It's what remains when you subtract fat from total weight.
This calculator uses the Boer formula, estimating lean mass from weight, height and sex — no bioimpedance scale needed.
Step-by-step example
An 80 kg, 1.80 m man: the formula estimates ~64 kg lean mass, implying ~16 kg (20%) fat.
What it's for
- Training: gaining lean mass is the goal of lifting; tracking it shows real progress.
- Protein: daily needs are often set per kg of body (or lean) mass.
- Medicine: some drug doses use lean mass instead of total weight.
It's a formula estimate — not a substitute for DEXA or professional assessment.
Examples
- Woman 60 kg, 1.65 m: estimated lean mass ~44 kg.
- Gaining muscle raises lean mass even if total weight barely changes.
Frequently asked questions
Why know lean body mass?
It helps set training, protein and medication targets.
Is lean mass just muscle?
No — it also includes bone, organs and water. Muscle is the largest part you can grow with training.
How does it relate to body fat %?
They are complementary: lean mass + fat mass = total weight. Know one, find the other.
Is lean mass the same as muscle?
No. It includes muscle, bone, organs, blood and body water — and water accounts for much of it.
I gained 2 kg of lean mass in a week. Is that real?
Almost certainly water. Real muscle gain happens over months, not days.
How do I avoid losing lean mass while dieting?
Strength training and adequate protein (1.6–2.2 g per kilo daily) do most of the work, plus enough sleep and a moderate deficit.
Are bioimpedance scales reliable?
For trends, yes, if measured under consistent conditions. For absolute values, DEXA is the practical reference.
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Updated on June 18, 2026 · by Rafael Rossi · Methodology & sources