Formula, in Body Composition
FFMI Formula: Kouri-Adjusted Fat-Free Mass Index
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.
3 variables. Published Mar 12, 2026. Updated May 10, 2026. By AI Fit Hub.
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
Run the numbers next
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Questions people ask next
What is the FFMI formula?
FFMI (Fat-Free Mass Index) is lean body mass divided by height in meters squared, with Kouri's height normalization added: FFMI = LBM_kg / (height_m)² + 6.1·(1.8 − height_m). The base term mirrors how BMI divides total mass by height squared, and the +6.1·(1.8−height) term corrects for the fact that shorter people naturally score higher on raw FFMI.
Is FFMI lean mass divided by height squared?
Yes — raw FFMI is lean body mass (kg) divided by height (m) squared, the same structure BMI uses for total mass. The Kouri-adjusted version adds 6.1·(1.8 − height_m) on top so values are comparable across different heights. Most fitness articles cite the raw version, so it is worth keeping them straight.
What is a good FFMI and what is the natural ceiling?
Reference ranges for men are roughly 18-20 for an average male, 22-23 for an advanced trained lifter, and about 25 as the natural ceiling, with values above 26 likely PED-assisted. For women the same equation applies but ranges drop about 3 units, averaging around 15 with a ceiling near 22.
How do I calculate lean body mass for FFMI?
Lean body mass is the kilograms of fat-free mass, obtained from a circumference equation (such as Boer), a DXA scan, or from body fat percentage via LBM = mass × (1 − BF%/100). For example, an 80 kg person at 22% body fat has LBM = 80 × 0.78 = 62.4 kg.
Where does the FFMI formula come from?
The height-normalized version comes from Kouri et al. (1995), published in Clinical Journal of Sport Medicine, which studied fat-free mass index in users and nonusers of anabolic-androgenic steroids and established the ~25 natural ceiling for men. The 1.8 m normalization reference is the academic standard, though some sources use 1.83 m or 1.7 m.
Sources
- Kouri EM, et al. Fat-free mass index in users and nonusers of anabolic-androgenic steroids , Clinical Journal of Sport Medicine (1995)
- Fat-free mass index and fat mass index percentiles in Caucasians aged 18-98 y , International Journal of Obesity (2002) — Schutz, Kyle & Pichard