How it works
FFMI estimates how much muscle you carry relative to your height. Unlike BMI, it accounts for body composition by subtracting fat mass.
The formula is:
FFMI = FFM(kg) / height(m)² + 6.1 × (1.8 − height(m))
The second term is a normalization adjustment for people shorter or taller than 1.8 m (about 5 ft 11 in). Without it, FFMI would systematically favor taller individuals.
Common reference points:
- 18–20: Typical for untrained or average adults.
- 20–22: Athletic, consistent training.
- 22–25: Very muscular; the upper end is often cited as a rough natural limit for most men.
- Above 25: Rare without long-term, elite genetics or performance-enhancing drugs.
Limitations
FFMI is a heuristic, not a diagnosis. The 25 "natural limit" comes from one influential study and does not apply cleanly to all ethnicities, body types, or measurement methods. Body-fat measurements themselves can be inaccurate, especially consumer scales and visual estimates. Use FFMI as one data point among many.