FFMI formula
Lean mass (kg) = weight × (1 − body fat % ÷ 100)
FFMI = lean mass ÷ height (m)²
Normalized FFMI = FFMI + 6.1 × (1.8 − height in m)
Worked example
A man who weighs 80 kg at 1.80 m with 15% body fat has 80 × 0.85 = 68 kg of lean mass. His FFMI is 68 ÷ 1.8² = 21.0. At exactly 1.80 m the normalized FFMI is the same.
FFMI ranges
| Level | Men | Women |
|---|
| Below average | Under 18 | Under 15 |
| Average | 18–20 | 15–17 |
| Above average | 20–22 | 17–18.5 |
| Excellent | 22–23.5 | 18.5–20 |
| Superior | 23.5–25 | 20–21.5 |
| Very rare | Over 25 | Over 21.5 |
These bands are general guides used by coaches, not medical categories. Your result depends heavily on how accurate your body fat estimate is.
Need a body fat estimate first? Use the body fat calculator. To fuel muscle gain, see the protein calculator.
Last reviewed October 2026.
Frequently asked questions
What is FFMI?
Fat-free mass index (FFMI) is like BMI but uses only your lean mass: everything except fat, including muscle, bone, organs and water. It shows how much muscle you carry for your height, which BMI cannot do.
How is FFMI calculated?
First find lean mass: weight × (1 − body fat % ÷ 100). Then divide it by your height in meters squared. The normalized FFMI adds 6.1 × (1.8 − height in m) so that tall and short people can be compared on the same scale.
What is a good FFMI?
For men, around 18–20 is typical, 20–22 shows above-average muscle and 22–25 is common for experienced lifters. For women, about 14–17 is typical. A 1995 study found most drug-free male lifters it measured were below about 25.
Do I need my body fat percentage?
Yes. FFMI needs an estimate of body fat. If you don't know yours, you can estimate it with the tape-measure method in the body fat calculator, then come back.
Is a higher FFMI always better?
Not necessarily. FFMI is a way to track muscle gain, not a health score. The best use is comparing your own number over time with the same body fat method.