FFMI Calculator
FFMI shows how much lean mass you carry for your height, which BMI cannot do. You need your body fat percentage for this one, so get it from our body fat calculator first.
What Is FFMI?
FFMI stands for fat free mass index. It works like BMI, but it uses only your lean mass. That makes it far better at telling a muscular person from an overweight one, because two people with the same BMI can carry very different amounts of muscle.
FFMI Formula
Taller people tend to score slightly lower on the raw formula. The normalized score corrects for that by adjusting everyone to a height of 1.80 m, which is why the calculator shows it as your main result.
What Is a Good FFMI?
In a study of 5,635 Swiss adults, the median FFMI among 18 to 34 year olds was 18.9 for men and 15.4 for women. The bands below are a rough guide we built around those medians. They are not a clinical classification.
| Normalized FFMI | Men | Women |
|---|---|---|
| Below the young-adult median | Under 18 | Under 14.5 |
| Around the median | 18-20 | 14.5-16.5 |
| Above average | 20-22 | 16.5-18.5 |
| Very muscular | 22 and up | 18.5 and up |
Does an FFMI of 25 Mean Steroids?
You will often see 25 described as a natural limit. The number comes from a 1995 study by Kouri and colleagues of 157 male athletes, in which many steroid users went above 25 while the non-users topped out around that level. It describes one group of men. It is not a test, and a score above 25 proves nothing about any individual. It may just reflect an inaccurate body fat estimate.
Why Your Body Fat Input Matters
FFMI is only as good as the body fat number you enter. If you underestimate your body fat by 5 points, your FFMI will come out too high. Use the same method each time, and treat small changes as noise. The lean body mass calculator shows the number behind this score, and the body recomposition calculator shows what happens when you lose fat without losing muscle. There is no single ideal body fat percentage, so read FFMI alongside your health markers rather than as a goal on its own.
Frequently Asked Questions
Find your lean mass in kilograms, then divide it by your height in meters squared. Someone with 65 kg of lean mass at 1.75 m has an FFMI of 21.2.
For muscular people, yes, because it ignores fat mass. It does need a body fat estimate, which BMI does not.
In the Swiss study above, the median for women aged 18 to 34 was 15.4. A higher score generally means more lean mass for your height.
Most differences come from whether the calculator shows raw or normalized FFMI, or from the body fat number you entered.