FFMI calculator
Fat-free mass index: how much lean mass you carry for your height. It’s BMI for people who lift.
No body fat number? Get one from the Navy body fat calculator.
Enter height, weight and body fat to calculate FFMI.
How FFMI is calculated
- Fat-free mass = weight × (1 − body fat %)
- FFMI = fat-free mass (kg) ÷ height (m)²
- Normalized FFMI = FFMI + 6.1 × (1.8 − height in m)
Example: 80 kg at 15% body fat and 1.78 m. Fat-free mass is 68 kg, FFMI is 68 ÷ 3.17 = 21.5, and normalized FFMI is 21.6.
FFMI reference ranges (men, normalized)
| FFMI | What it usually means |
|---|---|
| < 18 | Below average muscle mass |
| 18–20 | Average untrained adult |
| 20–22 | Noticeably trained |
| 22–23 | Excellent, years of consistent lifting |
| 23–25 | Superior, close to the drug-free ceiling found by Kouri et al. |
| > 25 | Rare without performance-enhancing drugs, or a body-fat under-estimate |
Because FFMI depends on your body-fat estimate, compare yourself with yourself. Track it every couple of months during a recomp or bulk, using the same body-fat method each time.
Questions people ask
What is FFMI?
Fat-free mass index is your lean mass (everything that isn’t fat) in kilograms divided by height in metres squared. It is like BMI but ignores fat, so it describes how much muscle you carry for your height.
What is a good FFMI?
For men, around 18–20 is typical for untrained adults, 20–22 is clearly trained, and 22–25 is very muscular. Women typically run about 3–4 points lower: roughly 14–17 average and 17–20 well trained.
Is an FFMI of 25 the natural limit?
Kouri et al. (1995, Clinical Journal of Sport Medicine) found that none of their drug-free male athletes had a normalized FFMI above about 25, while many steroid users did. It is a useful guide, not a hard rule: body-fat errors of a few points shift FFMI by a point or more.
What is normalized FFMI?
Taller people naturally score slightly higher, so Kouri’s paper adjusts to a 1.8 m reference: normalized FFMI = FFMI + 6.1 × (1.8 − height in metres).