FFMI Calculator
Calculate your fat-free mass index (FFMI) to gauge muscularity relative to height.
About the FFMI Calculator
FFMI is like BMI but for lean mass only: it divides everything that isn't fat by height squared, so it separates muscle from fat. Enter your height, weight and body-fat percentage; the result is normalised to a height of 1.8 m so tall and short people can be compared.
Kouri et al. (1995) studied 157 male athletes and found that drug-free men rarely exceed a normalised FFMI of about 25. The bands in the result follow that study.
The formula
FFMI = lean mass (kg) ÷ height (m)²; normalised = FFMI + 6.1 × (1.8 − height)
- lean mass
- weight × (1 − body fat % ÷ 100)
- height
- in metres
- 6.1 × (1.8 − height)
- adjustment to a 1.8 m reference height
Normalised FFMI bands (men)
| FFMI | Typical description |
|---|---|
| Under 18 | Below average |
| 18–20 | Average |
| 20–22 | Above average |
| 22–25 | Very muscular |
| Over 25 | Rare without drugs |
Women's values are typically about 3–4 points lower.
Worked example
180 cm, 80 kg, 15% body fat
- Lean mass: 80 × 0.85 = 68 kg
- FFMI = 68 ÷ 1.8² = 21.0
- Height is 1.8 m, so normalised FFMI is also 21.0: above average
Things to keep in mind
- Only as accurate as your body-fat estimate: bathroom scales and calipers can be several percentage points out.
- Not meant for children or for medical decisions.
Questions people ask
Do women use the same scale?
The formula is the same, but typical values are about 3–4 points lower.
How accurate is it?
Only as accurate as your body fat estimate. A DEXA scan is the most reliable everyday method.
FFMI or BMI?
BMI can't tell muscle from fat, so muscular people can read as overweight. FFMI needs a body-fat figure but describes muscle directly.