FFMI Formula (Kouri-adjusted)
Fat-Free Mass Index normalizes lean mass by height, like BMI does for total mass. Kouri's adjustment to 1.8 m makes values comparable across heights. Natural ceiling lands around 25 for men.
Formula
Copy the exact expression or work through it step by step below.
FFMI = LBM_kg / (height_m)² + 6.1·(1.8 − height_m) Variables
FFMI
Fat-Free Mass Index
Height-normalized lean mass score in kg/m². Reference: 18–20 average male, 22–23 advanced trained, 25 natural ceiling, >26 likely PED-assisted.
LBM_kg
Lean body mass
Kilograms of fat-free mass. From Boer equation, DXA, or LBM = mass × (1 − BF%/100).
height_m
Height
Meters (cm / 100). The Kouri term corrects for the fact that shorter people naturally score higher on raw FFMI.
Step By Step
- 1
Compute lean body mass either from a circumference equation, DXA scan, or BF%-derived calculation.
80 kg total, 22% body fat → LBM = 80 × 0.78 = 62.4 kg.
- 2
Convert height to meters and square it.
178 cm → 1.78 m → 3.1684 m².
- 3
Divide LBM by squared height.
62.4 / 3.1684 = 19.69 kg/m² raw FFMI.
- 4
Apply the Kouri normalization: add 6.1 × (1.8 − height_m).
6.1 × (1.8 − 1.78) = 0.122. Adjusted FFMI = 19.69 + 0.12 = 19.81.
Worked Example
Male, 80 kg, 22% body fat, 178 cm
Weight (kg)
80
Body fat (%)
22
Height (cm)
178
LBM = 62.4 kg. FFMI = 62.4 / 1.78² + 6.1·(1.8 − 1.78) = 19.69 + 0.12 = 19.81 kg/m²
FFMI 19.8 — average-to-recreational range. Trained natural lifter typically lands 22–24; 25+ warrants scrutiny.
Common Variations
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Sources & References
- Kouri EM, et al. Fat-free mass index in users and nonusers of anabolic-androgenic steroids — Clinical Journal of Sport Medicine (1995)
- Reference values for skeletal muscle mass and fat-free mass index — European Journal of Clinical Nutrition