Body composition
What is a good FFMI? Chart, natural limit and examples
Fat-free mass index (FFMI) tells you how much lean mass you carry for your height. Unlike BMI, it ignores fat, so it can separate a muscular lifter from someone who is simply heavy. That makes it one of the most useful single numbers for tracking muscle gain — and the number people argue about when they ask whether a physique is “natural”.
How FFMI is calculated
You need three numbers: body weight, height and body-fat percentage.
Lean mass (kg) = weight × (1 − body fat %)
FFMI = lean mass ÷ height (m)²
Normalized FFMI = FFMI + 6.1 × (1.8 − height in m)
The normalized version adjusts everyone to a height of 1.80 m. Taller people naturally carry a little less lean mass per square metre of height, so without the adjustment they would look less muscular than they are. When people quote FFMI ranges, they almost always mean the normalized figure.
What is a good FFMI for men?
These rule-of-thumb ranges for normalized FFMI are widely used for men:
| Normalized FFMI | Rating |
|---|---|
| Under 18 | Below average |
| 18–20 | Average |
| 20–22 | Above average |
| 22–23 | Excellent |
| 23–25 | Superior (near the drug-free limit Kouri observed) |
| Over 25 | Above the drug-free maximum Kouri observed (25) |
Most men who have trained consistently for a few years land somewhere between 20 and 23. A figure above 22 usually reflects years of well-planned training, good nutrition and favourable genetics.
Where the “natural limit” of 25 comes from
The number comes from a 1995 study by Kouri and colleagues in the Clinical Journal of Sport Medicine, which compared male athletes who used anabolic steroids with those who didn’t. The drug-free group averaged a normalized FFMI of about 21.8, and none of them exceeded 25.0. Many of the steroid users did.
That makes 25 a useful reference point, not a law. The study group was not every athlete who has ever lived, and a small number of people — especially heavier, very lean, genetically gifted lifters — may legitimately score slightly above it. Measurement error also matters a lot, as the next section shows.
Worked examples
| Lifter | Weight | Height | Body fat | FFMI | Normalized |
|---|---|---|---|---|---|
| Trained, average height | 80 kg | 180 cm | 15% | 21.0 | 21.0 |
| Tall and lean | 70 kg | 185 cm | 10% | 18.4 | 18.1 |
| Short, heavy and lean | 90 kg | 175 cm | 12% | 25.9 | 26.2 |
The third lifter is above 25. Before concluding anything, check the body-fat number: if they are really 16% rather than 12%, their normalized FFMI drops to about 25.
Why your body-fat estimate matters so much
FFMI is only as good as the body-fat percentage you feed it. Calipers, smart scales and even DEXA scans can differ by several percentage points for the same person. For an 80 kg lifter, each 3 points of body fat is 2.4 kg of lean mass — worth about 0.7 FFMI points at 180 cm.
- Use the same method each time, at the same time of day.
- Watch the trend over months rather than one reading.
- Be sceptical of very low body-fat readings from smart scales — they tend to inflate FFMI.
What about women?
Research on female FFMI is much thinner. Women typically score about 3–4 points lower than men with a similar training history, so a normalized FFMI of around 17–19 already reflects substantial muscle. There is no well-established equivalent of the male natural limit.
How to use FFMI
FFMI is best as a personal progress marker. If your normalized FFMI rises by 1 point over a year while your body fat stays steady, you have added meaningful muscle. Use it to judge your own training, not to police other people’s physiques.
Try the FFMI CalculatorFind your fat-free mass index and how close you are to the natural muscular limit.General fitness information, not medical advice. Check with a doctor or qualified coach before major changes to diet, supplements or training.