FFMI Calculator
FFMI is lean mass divided by height squared — BMI with the fat removed. It is the standard way to describe how muscular someone is independent of their body fat.
Your results
Entirely dependent on the accuracy of your body-fat figure — a 3-point error there moves FFMI by about 0.7. The often-quoted 'natural limit' of 25 is a soft observation from one study, not a biological ceiling.
How FFMI is calculated
Lean mass in kilograms divided by height in metres squared:
FFMI = lean kg ÷ (height m)²
The height-adjusted version adds a correction so that very tall and very short people can be compared: adjusted = FFMI + 6.1 × (1.8 − height m).
Because it uses lean mass rather than total weight, FFMI describes muscularity in a way BMI cannot — a lean 90 kg lifter and a 90 kg sedentary person of the same height get very different FFMI figures and identical BMIs.
About the 'natural limit'
You will see it claimed that an FFMI above 25 indicates steroid use. That comes from a 1995 study which observed that a group of drug-free bodybuilders clustered below about 25 while a group of steroid users sat above it.
It is a useful rough observation and not a hard boundary. Genuine outliers exist, particularly among very tall or heavily built people, and the figure is highly sensitive to the body-fat estimate — which for most people has an error of several points. Treat 25 as a region where claims deserve scrutiny, not as proof of anything.
Common questions
What is a good FFMI?
For men: around 18–20 is average, 20–22 above average, 22–25 excellent. For women: roughly 14–17 average, 17–19 above average, 19–21.5 excellent.
Is FFMI better than BMI?
For anyone who trains, yes — it separates muscle from fat, which BMI cannot.
What is the maximum natural FFMI?
Commonly quoted as about 25 for men, from a 1995 study. It is a soft observation with real exceptions, not a biological limit.
Why did my FFMI change when my weight did not?
Almost certainly your body-fat estimate changed. FFMI is very sensitive to it.
Track the numbers, not just calculate them
MyFitsy stores your weight, measurements and every session, so the figures above become a trend instead of a one-off.
