FFMI Calculator

Use this FFMI Calculator to estimate Fat-Free Mass Index from body weight, body-fat percentage, and height. FFMI expresses estimated fat-free mass relative to height.

Calculation Method

Fat-free mass = body weight × (1 − body-fat percentage ÷ 100)

FFMI = fat-free mass (kg) ÷ height (m)²

A commonly cited height-normalized version is:

Normalized FFMI = FFMI + 6.1 × (1.80 − height in meters)

Example

For someone weighing 80 kg at 15% body fat and 1.80 m tall:

Fat-free mass = 80 × 0.85 = 68 kg

FFMI = 68 ÷ 1.80² ≈ 20.99

Because the height is exactly 1.80 m, the normalized FFMI is also approximately 20.99.

Important Note

FFMI depends heavily on the accuracy of the body-fat percentage entered. It estimates total fat-free mass, not skeletal muscle alone, and should not be used to diagnose a medical condition or determine whether someone uses performance-enhancing drugs.

Sources

• Kouri et al. — Fat-Free Mass Index in Users and Nonusers of Anabolic-Androgenic Steroids
• Kyle et al. — Body Composition Interpretation and FFMI Reference Values