FFMI Calculator
Fat-Free Mass Index — assess muscle development relative to height
Enter Details
kg
cm
%
Results
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Enter your details and click Calculate.
Formula
FFMI = lean mass (kg) ÷ height² (m) Normalised FFMI = FFMI + 6.1 × (1.8 − height in m)
- lean mass (kg) — Total weight minus fat mass
- height (m) — Standing height
Example: 70 kg, 15% body fat, 1.78 m → lean mass 59.5 kg → FFMI = 18.8
Interpreting Your Result
< 17
Below average
Below typical muscular development
17–19.9
Average
Typical for recreational gym-goers
20–21.9
Above average
Noticeably muscular
22–24.9
Excellent
Exceptional natural development
≥ 25
Suspected enhancement
Rarely achievable naturally (Kouri et al.)
Frequently Asked Questions
What is a good FFMI for a natural athlete?
Research by Kouri et al. found naturals rarely exceed FFMI 25. Most advanced naturals fall between 20–24.
How does FFMI differ from BMI?
BMI doesn't distinguish muscle from fat. FFMI uses lean mass only, making it far more meaningful for athletes.