What FFMI tells you#
BMI cannot tell muscle from fat — a lean 90 kg lifter and an untrained 90 kg office worker score the same. FFMI fixes that by indexing only your fat-free mass to your height: lean mass (kg) divided by height (m) squared. It is the standard way to compare muscularity between people of different sizes.
FFMI benchmarks for men#
| Normalized FFMI | What it looks like |
|---|---|
| 16–17 | Below average muscle mass |
| 18–19 | Average, little training history |
| 20–22 | Clearly trains — solid recreational lifter |
| 23–25 | Very muscular, years of serious training |
| 26+ | At or beyond the typical natural maximum |
Women average roughly 3–4 points lower across the same descriptions.
Methodology and the “natural limit”#
The normalized score adjusts raw FFMI to a reference height of 1.8 m — adding 6.1 points per meter of difference — so taller and shorter lifters can be compared fairly. The famous 25 threshold comes from a study of steroid-tested bodybuilders in which almost no natural athlete exceeded a normalized FFMI of 25. Treat it as a strong benchmark rather than a law: your body fat estimate is the biggest source of error here, so measure it carefully with the tape method.