FFMI calculator (fat-free mass index)
Calculate your FFMI, the index that measures how much lean mass you carry for your height.
FFMI measures lean mass relative to height. ~19 is average, ~22 is very muscular and ~25 is seen as the natural limit for most men. It needs your body fat % (use the body fat calculator).
How the calculation works
First you get lean mass: weight × (1 − body fat%). Then FFMI = lean mass ÷ height²(m), similar to BMI but only for non-fat mass. The adjusted FFMI corrects for heights other than 1.80 m.
Examples
- Man 80 kg, 1.80 m, 15% fat: lean mass 68 kg → FFMI ≈ 21.
- FFMI ~18 is average; ~22 is quite muscular; ~25 is the typical natural ceiling.
Frequently asked questions
Is an FFMI above 25 possible naturally?
It is rare. Studies suggest ~25 as a ceiling for most drug-free men, though genetic exceptions exist.
FFMI vs BMI?
BMI uses total weight; FFMI uses only lean mass. So FFMI better reflects how muscular you are.
Do I need my body fat %?
Yes — FFMI starts from lean mass, which depends on body fat. Use the body-fat calculator first.
Is FFMI 25 really the natural limit?
It is a statistical reference from a small 1995 study, not a law. Genetics vary and body-fat measurement carries error.
Why does my FFMI vary so much?
Because it depends on body-fat percentage, and home bioimpedance scales can be off by 5 points or more.
Do the ranges apply to women?
Reference ranges for women sit about 3 points lower, due to natural differences in body composition.
What is FFMI actually useful for?
For tracking your own progress: it answers whether change came from muscle or fat, which weight alone cannot.
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Updated on June 30, 2026 · by Rafael Rossi · Methodology & sources