BMI can't tell muscle from fat. Fat-free mass index can: it measures how much lean tissue you carry for your height.
Normalised FFMI
21.6
Above average, trained
Raw FFMI
21.5
Lean mass
149.9lb
Lean mass = weight × (1 − body fat %). FFMI = lean mass (kg) ÷ height (m)². The normalised version adds 6.1 × (1.8 − height in m), a correction from Kouri et al. (1995) that stops tall people from being penalised, so scores can be compared across heights.
FFMI is only as good as your body fat number. A two-point error in body fat moves FFMI by around 0.4, so use a consistent method, like the tape-measure calculator, when tracking over time.
Fat-free mass index is lean mass in kilograms divided by height in metres squared. It is like BMI but ignores fat, so it measures how muscular you are for your height.
For men, 18–20 is average to above average, 20–22 is clearly trained, 22–25 is very muscular. For women the bands are roughly 3 points lower. The normalised value adjusts to a 1.8 m reference height.
A 1995 study by Kouri and colleagues found drug-free male athletes rarely exceeded a normalised FFMI of about 25. It is a useful rule of thumb, not a hard cut-off: measurement error in body fat alone can shift FFMI by a point or more.