FFMI calculator
Enter your weight, your height and your body-fat percentage: the calculator returns your fat-free mass, your FFMI and the FFMI normalised to 1.80 m, then places the result on the reference scale for your sex.
About 30 seconds
The formulas used
Fat-free mass (kg) = weight × (1 − body fat ÷ 100)
FFMI (kg/m²) = fat-free mass ÷ height in metres, squared
Normalised FFMI = FFMI + 6.1 × (1.80 − height in metres). Dividing by height squared mechanically favours shorter people; the correction brings everyone back to a common 1.80 m reference so two results can be compared.
For someone weighing 80 kg at 178 cm with 15% body fat, fat-free mass is 68.0 kg, FFMI is 21.5 and normalised FFMI is 21.6.
Index proposed by VanItallie and colleagues (American Journal of Clinical Nutrition, 1990); height normalisation and reference values from Kouri, Pope, Katz and Oliva, “Fat-free mass index in users and nonusers of anabolic-androgenic steroids” (Clinical Journal of Sport Medicine, 1995).
Normalised FFMI scale, men
| Interpretation | Normalised FFMI |
|---|---|
| Below average | Below 18 |
| Average | 18 to 20 |
| Above average | 20 to 22 |
| Excellent | 22 to 25 |
| Rarely reached naturally | 25 and above |
The 25 mark comes from the original study: among 157 men who had never used steroids, none went past it, while a share of the users reached 30. It is a statistical marker, not an individual verdict — a very tall or very heavy athlete, or one whose body fat has been underestimated, can cross 25 without ever having taken anything. For women the whole scale sits roughly three points lower.
How much the body-fat estimate moves the result
| Body fat | Fat-free mass | Normalised FFMI |
|---|---|---|
| — | — | — |
| — | — | — |
| — | — | — |
Weight and height are easy to measure precisely; body fat is not. The table shows what your result becomes if the estimate is three points off either way — the usual error of a bioimpedance scale. Two FFMI figures are only worth comparing when they come from the same measurement method.
Getting a result you can use
Weigh yourself in the morning, before eating and after going to the bathroom, and measure your height barefoot with your heels against the wall. These two values are the easy ones to keep consistent.
For body fat, always stay with the same method: DEXA (±1 to 2 points), hydrostatic weighing, skinfolds taken by the same person (±3 points), bioimpedance (±4 to 5 points). Switching methods between two measurements creates an FFMI change that never happened.
Follow the trend over several months rather than a single figure. For someone already training seriously, a realistic gain is 1 to 2 kg of fat-free mass a year, which is roughly 0.3 to 0.6 of an FFMI point.
Read the fat-free mass definition · See all calculators
Frequently asked questions
Here are some common questions about the FFMI calculator.
Take the fat out of your total weight to get fat-free mass, then divide it by your height in metres squared. For 80 kg, 178 cm and 15% body fat: 68 kg of fat-free mass divided by 1.78² gives an FFMI of 21.5.
For men, a normalised FFMI around 19 is average, 20 to 22 describes someone training seriously, and 22 to 25 is a high athletic level. For women, take about three points off each of those marks.
Dividing mass by height squared gives shorter people a built-in advantage on the raw index. The 6.1 × (1.80 − height) correction puts everyone on the same 1.80 m reference, which is what makes two people of different heights comparable.
No. It is a statistical signal, not a test. In the original study no non-user went past 25, but the sample was small and the whole calculation rests on the body-fat measurement — an estimate that is a few points too low is enough to push someone over the line.
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