FFMI Calculator
Work out your fat-free mass index from weight, height and a body fat estimate, and the height-normalised figure from Kouri and colleagues.
Result
Enter weight, height and body fat percentage to see the result.
https://calcgallery.com/body-composition/ffmi-calculator/
How to use the FFMI Calculator
- Enter your weight and height.
- Enter a body fat percentage from whatever method you have, such as a DEXA scan, callipers, a tape method or a bioimpedance scale.
- Read the normalised FFMI, the plain FFMI and your fat-free mass. The normalised figure is the one to compare between people of different heights.
How it is calculated
Fat-free mass is everything that is not fat: muscle, bone, organs and water. From your weight and body fat percentage:
fat-free mass = weight × (1 − body fat)FFMI = fat-free mass ÷ height²normalised = FFMI + 6.3 × (1.80 − height)Weight is in kilograms and height in metres, so FFMI is in kg/m², the same units as BMI. The page converts pounds and feet and inches first.
Where the normalisation comes from
The height correction comes from a 1995 study by Kouri, Pope, Katz and Oliva of 157 male athletes. They adjusted every value to the equivalent for a 1.80 m man, so that athletes of different heights could be compared. The abstract gives that correction as 6.3 × (1.80 m − height).
How good is the number?
The index is exact arithmetic on your inputs, but the body fat input is not exact. Different methods can disagree by several percentage points on the same person, and any error in body fat carries straight into fat-free mass and the index. Comparing results over time from the same method, measured the same way, is more meaningful than comparing a single number with someone else’s.
With your numbers
- Fat-free mass = 81.65 kg × (1 − 18%) = 66.95 kg
- FFMI = 66.95 ÷ 1.778² = 21.2
- Normalised = 21.18 + 6.3 × (1.80 − 1.778) = 21.3
Quick reference
Only as accurate as the body fat figure entered: any error there carries straight into the index.
| Example | Normalised FFMI (to 1.80 m) |
|---|---|
| 70 kg, 175 cm, 15% | 19.7 |
| 80 kg, 175 cm, 15% | 22.5 |
| 80 kg, 180 cm, 12% | 21.7 |
| 95 kg, 190 cm, 12% | 22.5 |
| 60 kg, 165 cm, 25% | 17.5 |
| 180 lb, 5 ft 10 in, 18% | 21.3 |
| 200 lb, 6 ft 0 in, 15% | 22.9 |
Common questions about the FFMI Calculator
- What is FFMI?
- Fat-free mass index is like BMI with the fat taken out: fat-free mass in kilograms divided by height in metres squared. Two people with the same BMI can have very different FFMIs if one carries more muscle and the other more fat, which is why the index is used to describe muscularity rather than size.
- Why normalise to 1.80 m?
- So that people of different heights can be compared on one scale, Kouri and colleagues adjusted each value to its equivalent for a man 1.80 m tall. At exactly 1.80 m the correction is zero; shorter people get a small addition and taller people a small deduction.
- Why does this page use 6.3 when other calculators use 6.1?
- The abstract of the 1995 paper that introduced the correction states it as 6.3 × (1.80 m − height). Many calculators use 6.1 instead. The full text of the paper was not available to check, so the page follows the figure the paper's own abstract prints and flags the difference. For most heights the two differ by well under a tenth of a point.
- Is there a natural limit to FFMI?
- This page does not state one. The 1995 study was a small sample of male athletes and was designed around a specific screening question. Treat the index as a description of your own body composition over time, not as a ceiling or a test.
- Does it work for women?
- The arithmetic works for anyone, but the normalisation was worked out on men and to the height of a man of 1.80 m. The plain FFMI, without the height correction, is the more neutral figure to track for women.