FFMI calculator (fat-free mass index)
Work out your fat-free mass index (FFMI) and normalized FFMI from your height, weight and body fat. A BMI that counts only muscle, bone and organs.
What FFMI is
FFMI is like BMI, but it counts only your fat-free mass: muscle, bone, organs and water. It’s your fat-free mass in kilograms divided by your height in meters squared [1]:
- Fat-free mass = weight × (1 − body fat % ÷ 100)
- FFMI = fat-free mass (kg) ÷ height (m)²
- Normalized FFMI = FFMI + 6.1 × (1.8 − height in m)
Taller people have a slightly higher FFMI for the same build. Normalized FFMI adjusts everyone to a height of 1.8 m (5 ft 11 in) so they can be compared.
The 25 limit
In the study that introduced it, men who had never used anabolic steroids had a normalized FFMI of up to about 25. Many steroid users were above that, some over 30 [1]. It’s a rough ceiling for men, not a target. The study didn’t include women.
How accurate is it?
FFMI is only as good as your body fat number. If body fat is 3 points too low, FFMI comes out about 0.7 too high for someone of average size. Use the same body fat method every time, and compare your FFMI with your own earlier results rather than with other people.
Don’t know your body fat? Start with the body fat calculator. To raise your FFMI, follow the muscle goal.
Questions
What is a good FFMI?
Higher means more muscle for your height, and it goes up as you train. Rather than chasing a number, compare your own FFMI every few months: if it’s rising, you’re building muscle.
Is an FFMI of 25 the natural limit?
In a study of male athletes, men who had never used steroids had a normalized FFMI of up to about 25, while many steroid users were above it. A few people exceed 25 naturally, and a body fat estimate that’s too low will also push FFMI up.
Why is FFMI better than BMI for lifters?
BMI counts all your weight, so a muscular person can come out as overweight. FFMI removes the fat first, so it only rises with muscle (and bone and water).
How do I find my body fat percentage?
Use the body fat calculator on this site with a tape measure, or a DEXA scan if you have access to one. The same method each time matters more than which method you use.
General information, not medical advice. If you have a health condition, are pregnant or take medication, check with your doctor.
Sources
- [1]Kouri et al., Fat-free mass index in users and nonusers of anabolic-androgenic steroids, Clinical Journal of Sport Medicine (1995). https://doi.org/10.1097/00042752-199510000-00003