Lean Body Mass Calculator
Estimate your lean body mass — muscle, bone, organs, and water, everything but fat — using the Boer formula.
The Boer formula
Women: LBM = 0.252×kg + 0.473×cm − 48.3
If you know your body fat percentage, LBM = weight × (1 − body fat) is more accurate — get body fat from the body fat calculator.
Man, 178 cm, 80 kg: 0.407×80 + 0.267×178 − 19.2 = 32.6 + 47.5 − 19.2 = ~60.9 kg lean, about 19 kg fat (24%).
Why lean mass is the number to protect
When people say they want to "lose weight," they almost always mean lose fat while keeping muscle. Lean body mass is that muscle-plus-everything-else — and it's the engine of your metabolism and strength. In a diet, protecting LBM is the whole game: hit your protein target (often set per pound of LBM), keep lifting, and avoid crash deficits that strip muscle along with fat. Tracking LBM alongside body fat over time shows whether a program is working even when scale weight barely moves.
Frequently asked questions
What is lean body mass?
Everything that isn't fat — muscle, bone, organs, water. Total weight minus fat mass.
Why does it matter?
It drives metabolism and strength; preserving it while losing fat is the goal of good dieting.
How is it calculated?
Boer formula from height/weight/sex, or weight × (1 − body fat %) if you know your body fat.
Related calculators
Medical disclaimer: A formula-based estimate, not a clinical measurement or medical advice. Formula: Boer (1984). Last reviewed: July 2026.