Lean Body Mass Calculator
Estimate your lean body mass and fat mass (Boer formula).
Result
Lean body mass (kg)
56.0
Fat mass (kg)
14.0
How it works
Lean body mass is everything that is not fat: muscle, bone, organs, blood and water. This calculator uses the Boer formula, which estimates it from height, weight and sex, and reports the fat mass as the remainder. It is the number that explains why the scale misleads during training. Gaining muscle while losing fat can leave total weight unchanged for weeks even as the body transforms — a plateau on the scale that is real progress in composition. Lean mass also drives metabolism, since muscle and organs burn energy at rest while fat burns very little. That is why preserving lean mass during a diet matters so much: lose it, and the resting metabolic rate falls with it, making the weight easier to regain.
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Frequently asked questions
What is lean body mass?
Your total weight minus body fat — muscle, bone, water and organs.
Is this exact?
It's an estimate from a formula; a body-composition scan is more precise.
Why is lean body mass used for drug dosing?
Because many drugs distribute through lean tissue rather than fat, so dosing on total weight can overdose a person carrying more fat. Anaesthetics in particular are often calculated on lean mass for exactly this reason.
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