FFMI Calculator (Fat-Free Mass Index)
Work out your Fat-Free Mass Index from weight, height and body-fat percentage, with the height-adjusted FFMI and a reference band.
How it works
FFM = weight × (1 − bodyfat%/100); FFMI = FFM ÷ height(m)²; adjusted FFMI = FFMI + 6.1 × (1.8 − height(m))
FFMI (Fat-Free Mass Index) strips the fat out of your weight and asks how much lean mass you carry for your height. First it finds fat-free mass — everything that is not body fat — then divides by height squared, exactly like BMI but on muscle instead of total weight. The adjusted figure normalises to a 1.8 m frame so tall and short lifters can be compared on the same scale. Drug-free men rarely push a normalised FFMI much past 25, which is why very high values raise questions.
Worked example
An 80 kg man at 178 cm and 15% body fat carries 68 kg of fat-free mass. At 1.78 m that is 68 ÷ 1.78² ≈ 21.5 FFMI, adjusted to about 21.6 — squarely in the above-average band for a natural lifter.
Frequently asked questions
What FFMI counts as “muscular”?
Roughly 20–22 is above average, 22–23 is excellent and near the natural ceiling for most men. Values above about 25 (normalised) are uncommon without performance enhancement, though genetics and frame play a part.
Why use FFMI instead of BMI?
BMI counts all weight the same, so a lean, muscular athlete can read as “overweight”. FFMI ignores fat entirely and measures lean mass for height, which is far more useful for tracking training.
Do I need an accurate body-fat number?
Yes — FFMI is only as good as your body-fat estimate, since that decides how much of your weight counts as lean. A DEXA or good caliper reading beats a bathroom-scale guess.
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Educational estimate, not medical advice. Consult a qualified professional for health decisions.