How to use it
- Type your Body weight and choose its unit, kilograms or pounds.
- Type your Height and choose centimetres or inches.
- Type your Body fat as a percentage, from the most reliable measurement you have.
- Read the Normalized FFMI at the top, then the Fat-free mass index (FFMI) and the How the result is worked out list.
How the index is calculated
Kouri, Pope, Katz and Oliva defined the fat-free mass index in 1995. It divides the body's lean mass by height squared, so that people of different heights can be compared. Their abstract adds a correction of 6.3 × (1.80 m − height) to bring each value to the height of a man of 1.80 m. That correction is the normalized FFMI on this page.
This is not medical advice. An FFMI on its own does not show a health problem, and body fat from a home scale is an estimate. Ask a doctor or a dietitian about your body composition.
Fat-free mass = weight × (1 − body fat ÷ 100)
FFMI = fat-free mass ÷ height² (height in metres)
Normalized FFMI = FFMI + 6.3 × (1.80 − height)- Pounds are converted with 1 lb = 0.45359237 kg, and inches with 1 in = 2.54 cm, before the formulas run.
- The result depends on the body fat you type. A change of one percentage point in body fat changes the fat-free mass by one percent of your weight.
What the figure does and does not show
Kouri et al. measured 157 male athletes: 83 who used anabolic-androgenic steroids and 74 who did not. The normalized FFMI of the 74 non-users extended up to 25.0. The authors called their work preliminary, and the number describes that sample only. It is not a standard that every athlete should reach, a target, or a verdict on anyone's training or drug use.
The index does not separate muscle from water, glycogen or bone. Age and sex are not part of the formula, and the paper studied men only, so a comparison with women or older people needs other data.
Worked example: 80 kg, 175 cm, 15 % body fat
The fat-free mass is 80 × (1 − 0.15) = 68.0 kg. The height squared is 1.75² = 3.0625 m², so the FFMI is 68.0 ÷ 3.0625 = 22.2 kg/m².
The height correction is 6.3 × (1.80 − 1.75) = 0.315, so the normalized FFMI is 22.204 + 0.315 = 22.519, shown as 22.5 kg/m².
| Measure | Value |
|---|---|
| Fat-free mass | 68.0 kg |
| Fat mass | 12.0 kg |
| FFMI | 22.2 kg/m² |
| Normalized FFMI | 22.5 kg/m² |
Frequently asked questions
What is a good FFMI?
The index does not give a good or a bad score on its own. In the 1995 paper the normalized FFMI of the non-using athletes reached 25.0, but that describes one sample of men, not a target for anyone.
Why is the FFMI normalized to a height of 1.80 m?
Kouri et al. added the correction so that values can be compared between people of different heights. The paper describes it as a slight correction to normalize the values to the height of a 1.8 m man.
Is the FFMI the same as the body mass index?
No. Body mass index uses total weight and height only, while the FFMI uses fat-free mass, so it leaves out body fat. The two figures can point in different directions for the same person.
Why does a small change in body fat change the result so much?
The fat-free mass is weight multiplied by one minus the body fat fraction. Each percentage point of body fat moves the fat-free mass by about one percent of your weight, and that difference carries into the FFMI.
Can I use pounds and inches?
Yes. Choose lb for the weight and in for the height. The calculator converts both with the exact factors, 0.45359237 kg per pound and 2.54 cm per inch, before it works out the index.
Sources
Figures and text last checked on Tuesday, November 10, 2026.