FFMI Calculator (Fat-Free Mass Index)

What this calculates

FFMI normalizes lean mass by height, like BMI but for muscle. It's the favorite metric for distinguishing 'big' from 'jacked' — a 6'2" 200 lb lifter has a different FFMI than a 5'6" 200 lb lifter. Natural drug-free FFMI typically caps around 25; values significantly above are rare without enhancement.

Formula & how it works

Lean mass (kg) = weight × (1 − bodyfat%). FFMI = lean_mass / height(m)². Adjusted FFMI = FFMI + 6.1 × (1.8 − height_m) — normalizes to 1.8m height.

Worked example

85 kg, 12% bodyfat, 1.80 m. Lean = 74.8 kg. FFMI = 74.8 / 1.8² = 23.1. Adjusted = 23.1.

Frequently asked questions