Body composition
FFMI
Calculate your fat-free mass index to assess your natural muscular potential.
Normalised FFMI
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Raw FFMI
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Lean mass
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kg
Estimated natural limit (Kouri 1995): men ≈ 25, women ≈ 22.
What is FFMI?
FFMI (Fat-Free Mass Index) is a measure of muscle mass relative to height, similar to BMI but applied to lean mass. It was introduced by Kouri et al. in 1995 to evaluate natural muscular potential without the use of anabolic steroids.
How is it calculated?
First, lean mass is calculated by subtracting fat from total weight. Then it is divided by height squared. Normalised FFMI is adjusted to a height of 1.80 m for standard comparison.
Formula
FFMI = Lean mass(kg) ÷ Height²(m) · Normalised FFMI = FFMI + 6.1 × (1.80 − height)⚠️ Limitations
An FFMI > 25 (men) does not imply drug use, but is statistically unusual. FFMI is a guiding tool, not a diagnostic one.
FAQ
What is the maximum natural FFMI?
The Kouri (1995) study set ~25 as the upper limit for natural athletes. Most reach 22–23.
Can I increase my FFMI with training?
Yes, but there is a genetic ceiling. Beginners have more room for improvement than advanced athletes.
Is FFMI the same for women?
Reference values are lower: the natural limit for women is around FFMI 22.
Do I need to know my body fat % to calculate it?
Yes. You can estimate it with our body fat calculator using the Navy method.