Evaluate your body composition with the Fat-Free Mass Index — a more accurate metric than traditional BMI for assessing muscularity.
Enter your data and click calculate to see your results.
Understand the science behind FFMI and how to interpret your results.
The Fat-Free Mass Index is a metric developed to evaluate the amount of lean mass relative to height, independent of body fat.
Unlike traditional BMI, FFMI can distinguish between muscular individuals and those with excess fat — two groups that may have the same BMI but completely different body compositions.
Fat-Free Mass:
Base FFMI:
Normalized FFMI (adjusted to 1.80m):
| FFMI | Men | Women |
|---|---|---|
| 16-17 | Below average | Average |
| 18-19 | Average | Above average |
| 20-21 | Above average | Excellent |
| 22-23 | Excellent | Elite/Suspect |
| 24-25 | Natural limit | Highly suspect |
| 26+ | Suspect | — |
FFMI was popularized by the study of Kouri, Pope, Katz, and Oliva (1995), published in the Clinical Journal of Sport Medicine.
The researchers analyzed 157 male athletes (83 steroid users and 74 non-users) and found that an FFMI of 25 represented a limit rarely exceeded by natural athletes.
View study on PubMedFFMI accuracy depends on correct body fat measurement. Available methods:
Most accurate: DEXA scan, hydrostatic weighing, Bod Pod
Moderately accurate: Bioimpedance (smart scales), skinfold calipers
Estimates: Visual comparison with reference photos, online calculators based on measurements
While FFMI 25 is often cited as the "maximum natural limit," there is scientific debate about this value:
• Some genetically gifted individuals may exceed it naturally
• The original study had methodological limitations
• Elite athletes from the pre-steroid era (before 1940) occasionally exceeded this value
FFMI should be used as a guiding reference, not an absolute diagnosis.