Fat-Free Mass Index (FFMI)
Measure muscularity relative to height, adjusted for body fat
What This Calculator Measures
The Fat-Free Mass Index (FFMI) is a measure of muscularity normalized for height, similar to how BMI normalizes weight for height. Unlike BMI, FFMI only considers lean mass, making it a far superior metric for assessing how muscular someone is relative to their frame.
How It Works
**FFMI = Lean Mass / Height(m)²**
**Adjusted FFMI = FFMI + 6.1 x (1.8 - Height(m))**
The height adjustment normalizes the score so that taller and shorter individuals can be compared fairly.
| Adjusted FFMI | Classification |
|---|---|
| Below 18 | Below average muscularity |
| 18 - 20 | Average (typical male) |
| 20 - 22 | Above average (consistent training) |
| 22 - 25 | Excellent (years of serious training) |
| 25+ | Suspicious (likely exceeds natural limit) |
The Natural Limit
Research by Kouri et al. (1995) found that an FFMI of approximately 25 represents the upper limit of muscularity achievable without performance-enhancing drugs. Pre-steroid-era bodybuilders and modern drug-tested athletes rarely exceed this threshold.