What is FFMI?
Fat-Free Mass Index (FFMI) is an alternative to BMI that quantifies the amount of muscle mass a person carries relative to their height. Unlike BMI, which penalizes muscular individuals by labeling them "overweight," FFMI rewards muscle mass. It is widely considered the gold standard for tracking natural hypertrophy progress.
The "Natural Limit" (25.0)
The Kouri Study (1995)
Researchers analyzed 157 male athletes, comprising 83 users of anabolic steroids and 74 non-users. They found that not a single non-user exceeded an FFMI of 25.0. Conversely, many steroid users scored well into the 30s.
This finding established "25.0" as a widely accepted upper threshold for natural human potential. While genetic outliers exist, sustaining a lean condition with an FFMI above 25 is incredibly difficult without hormonal assistance.
The FFMI Scale (Men)
| FFMI Score | Category | Description |
|---|---|---|
| < 18 | Below Average | Lightly muscled or skinny. |
| 18 - 20 | Average | The average male gym-goer. |
| 20 - 22 | Athletic | Noticeable muscular development. |
| 22 - 23 | Natural Bodybuilder | Excellent natural development. |
| 23 - 25 | Genetic Elite | Near the natural limit. |
| > 25 | Suspicious | Likely enhanced / steroid use. |
Why Use "Normalized" FFMI?
Measurement of FFMI inevitably increases with height. A 6'4" man will almost always have a higher raw FFMI than a 5'6" man of equal relative muscularity. To fix this, researchers developed the Normalized FFMI equation:
This adjusts every individual to the height of a 1.8m (roughly 5'11") reference man, allowing for fair comparison between short and tall lifters.
Related Tools
Calculate steps before finding your FFMI.
Frequently Asked Questions
What is a good FFMI score?
Can I get an FFMI above 25 naturally?
Why does the calculator adjust for height?
What if my FFMI is low?
Tools & Data Verified by the EverydayCalculators Medical Research Team.
Last updated: December 2026.