If you're a weightlifter, BMI is pretty much useless for you. BMI doesn't distinguish between muscle and fat mass, it looks only at your total body weight versus your height. The FFMI (Fat Free Mass Index) adjusts for this by calculating how much muscle mass you have relative to your height.
It's a way to gauge your physique and whether your muscle-building goals are achievable without steroids.
The "adjusted" version normalizes for differences in height, that way you can compare yourself to someone 6 inches taller or shorter.
Not sure what your body fat percentage is? Use our body fat calculator first.
What is Fat Free Mass Index?
FFMI is like BMI, except it uses your lean body mass (LBM), which is your weight excluding body fat. This means you are not penalized for having muscle.
You need to know your body fat percentage to use this calculator. Then, it calculates how much lean body mass you have per square meter of height.
How FFMI is Calculated
First you calculate your lean mass (what you weigh minus your fat), then divide by height squared. Finally, the result is adjusted for height so that people of different sizes can be compared - the number 6.3 normalizes everyone to a height of 1.8m (about 5'11").
Lean Mass (kg) = Weight (kg) × (1 - Body Fat% / 100)
FFMI = Lean Mass (kg) / Height (m)²
Adjusted FFMI = FFMI + 6.3 × (1.8 - Height (m))
FFMI Categories
| Category | Men | Women |
|---|---|---|
| Below Average | < 18 | < 13 |
| Average | 18-20 | 13-15 |
| Above Average | 20-22 | 15-17 |
| Excellent | 22-23 | 17-18 |
| Superior | 23-26 | 18-21 |
| Likely Enhanced | > 26 | > 21 |
The Natural Limit
Studies of bodybuilders from the pre-steroid era (pre-1959) found that even the best athletes topped out around an FFMI of 25. Nobody exceeded that.
That doesn't mean 26 is impossible naturally, but it is the ceiling for almost everyone. If you see someone with an FFMI above 26, they're either a (genetic) freak of nature, or on steroids.
Want to dig deeper into your body composition? Check out our lean body mass calculator or body fat calculator.