FFMI Calculator (Fat-Free Mass Index)
Calculate raw and height-normalized fat-free mass index from weight and body-fat percentage, with the natural-limit context from the Kouri research.
Results
- Lean body mass
- 68 kg
- Bodyweight x (1 - 15% body fat)
- Fat mass
- 12 kg
- Fitness range
- Raw FFMI
- 21
- Lean mass (kg) / height (m)2
- Normalized FFMI
- 21
- Adjusted to a 1.8 m reference height
- Reference
- Above average (men)
- Kouri-style reference bands
Normalized FFMI reference bands (men, Kouri et al.)
| FFMI | Reference |
|---|---|
| < 18 | Below average |
| 18 - 19 | Average |
| 20 - 21 | Above average |
| 22 - 23 | Excellent |
| 24 - 25 | Superior |
| 26+ | Exceptional / suspicious without drugs |
How it works & limitations
Formulas
FFMI = lean mass (kg) / height (m)2 Normalized FFMI = FFMI + 6.1 x (1.8 - height in meters) The adjustment removes the small height advantage from raw FFMI.
The natural-limit context
Kouri et al. found elite natural male bodybuilders around 25, while values above 25 were almost exclusively seen in users of anabolic-androgenic steroids. Female bands are commonly adapted about 4-5 points lower but are less validated. These are population context, not individual verdicts - body-fat measurement error directly changes the result.
Tracking advice
Use the same body-fat method every time (ideally DEXA or a skilled skinfold measurer), measure under the same conditions, and watch the trend rather than a single number. A one-point FFMI change is usually within measurement noise.
Sources
Last updated 2026-08-13
- Kouri, E. M., Pope, H. G., Katz, D. L., & Oliva, P. (1995). Fat-free mass index in users and nonusers of anabolic-androgenic steroids. Clinical Journal of Sport Medicine, 5(4), 223-228.
FFMI depends entirely on your body-fat estimate. Interpret it with the measurement method and its error in mind, and never use it to judge or accuse anyone.
Frequently asked questions
What is a natural FFMI limit?
In the Kouri et al. study, elite natural male bodybuilders reached about 25, while values above 25 were almost exclusively seen in users of anabolic-androgenic steroids. Women typically score roughly 4-5 points lower. Treat these as population context, not individual verdicts.
Why is FFMI normalized to height?
Raw FFMI slightly favors taller athletes. The standard adjustment (+6.1 x (1.8 - height in meters)) normalizes to a 1.8 m reference so shorter and taller athletes can be compared fairly.