Last updated: 3 October 2026
Reviewed by Jordan Morley, FA Level 2 Football Coach
FFMI (Fat-Free Mass Index) = lean body mass (kg) ÷ height (m)². It measures the amount of lean mass relative to height, analogous to BMI but for muscle. A natural male bodybuilder rarely exceeds FFMI 25; values above 25 are extremely rare naturally and are associated with anabolic steroid use in research. Average untrained male FFMI is approximately 19-20; trained naturals typically reach 21-24. The metric was popularised in a 1995 study comparing modern bodybuilders to pre-steroid era athletes. Female FFMI values are approximately 4 points lower.
- Lean mass (kg) / height (m)²
- Male natural ceiling ~25 FFMI
- Average trained natural male 21-24
- Values above 25 very rare without pharmaceutical assistance
In practice
FFMI (fat-free mass index) is popular in bodybuilding circles as a rough ceiling check on 'natural' muscularity — an FFMI around 25 is considered an approximate natural genetic limit for most men without performance-enhancing drugs, though factors like height, bone structure and training history mean it's a loose guideline rather than a precise diagnostic test.
FAQ
What is considered a high natural FFMI?
Around 23-25 is considered a very muscular natural FFMI for men; values significantly above 25 are often (though not always, depending on height and frame) associated with performance-enhancing drug use.
Is FFMI a perfectly reliable indicator of steroid use?
No — it's a rough statistical guideline, not a diagnostic tool; exceptionally gifted genetics, favourable height/frame, and measurement inaccuracy in body fat percentage can all push natural FFMI figures higher than typical.