Fat Free Mass Index Calculator

The fat-free mass index (FFMI) is like BMI, but it counts only your fat-free mass. It shows how much muscle and other lean tissue you carry for your height.

Your details

Sex
kg
cm
%

Don't know your body fat %? Estimate it with the Body Fat Calculator. The result is only as accurate as that number.

Your results

Enter your weight, height and body fat % to see your FFMI.

How to use it

  1. Choose your units, then enter your sex, weight, height and body fat %.
  2. Read your FFMI and your height-normalized FFMI.
  3. Use the same body fat method each time if you track it. A different method can shift the result by a point or more.

How it's calculated

FFMI. Fat-free mass divided by height squared (VanItallie et al., 1990):

  • Fat-free mass = weight × (1 − body fat % ÷ 100)
  • FFMI = fat-free mass (kg) ÷ height (m)²

Height-normalized FFMI. Kouri and colleagues (1995) adjusted FFMI to a height of 1.80 m:

normalized FFMI = FFMI + 6.3 × (1.80 − height in m)

The calculator uses the coefficient printed in the published abstract.

Example: 85 kg at 15% body fat and 1.80 m tall gives 72.3 kg of fat-free mass and an FFMI of 22.3. At exactly 1.80 m, the normalized value is the same.

The “25” reference. Kouri and colleagues measured 157 male athletes: 83 steroid users and 74 non-users. The normalized FFMI of the non-users went up to 25.0; many users went above it. The meter marks 25 for reference.

Limits. FFMI inherits every error in your body fat number, and fat-free mass includes water, bone and organs, not just muscle. The reference value comes from one study of men.

Sources

  1. Kouri, E. M., Pope, H. G., Katz, D. L., & Oliva, P. (1995). Fat-free mass index in users and nonusers of anabolic-androgenic steroids. Clinical Journal of Sport Medicine, 5(4), 223–228.
  2. VanItallie, T. B., Yang, M. U., Heymsfield, S. B., Funk, R. C., & Boileau, R. A. (1990). Height-normalized indices of the body's fat-free mass and fat mass: potentially useful indicators of nutritional status. American Journal of Clinical Nutrition, 52(6), 953–959.

Questions

What is a good FFMI?

It depends on your sex, training and how you measured body fat. In the 1995 study of male athletes, the drug-free athletes reached a normalized FFMI of up to 25. Most people who don't train sit well below that.

Is an FFMI over 25 proof of steroid use?

The value 25 comes from one 1995 study of 157 men. An individual score cannot determine steroid use. Body fat measurement error can move the score across that reference.

What does height-normalized mean?

Taller people tend to score a bit lower on plain FFMI. The study added a small correction that adjusts everyone to a height of 1.80 m, so people of different heights compare more fairly.

Does it work for women?

You can calculate it, but the 25 reference and the height correction come from a study of men. For women, the most useful comparison is with your own earlier results.

Updated November 9, 2026.