FFMI Calculator

FFMI stands for Fat-Free Mass Index. It is your lean (fat free) body mass divided by your height in metres squared, so it tells you how muscular you are relative to your height. Think of it as a BMI that ignores fat and only counts muscle, bone and organs.

Taller people tend to score a lower raw FFMI for the same build, so the normalized version adjusts everyone to a 1.8 m reference height using the formula FFMI + 6.1 times (1.8 minus your height in metres). At exactly 1.8 m the two numbers are identical; below 1.8 m the normalized value goes up and above it the value goes down.

Roughly, under 18 is below average, 18 to 20 is average, 20 to 22 is above average, 22 to 23 is excellent and 23 to 26 is very muscular. Research on drug-free lifters found a normalized FFMI around 25 is near the natural ceiling, so values much above 26 in a lean person are often a sign of enhancement.

Use any method you trust: skinfold calipers, the US Navy tape method, bioimpedance scales or a DEXA scan. FFMI is only as accurate as the body fat figure you feed it, so a measured value beats a guess.

For muscular people, yes. BMI counts all your weight as if it were fat, so a fit, heavily muscled person can be labelled overweight. FFMI strips out fat and measures lean mass instead, which is a fairer gauge of muscularity, though it needs a body fat reading that BMI does not.

No. The calculation runs entirely in your browser. Your weight, height and body fat figures never leave your device.