Home/Tools/FFMI Calculator

FFMI Calculator: How Close Are You to the Natural Limit?

Paul Hummel Last reviewed October 6, 2026 4 min read
Calculator

Calculate FFMI

Formula and normalization by Kouri et al. (1995).

Don’t know your body fat? Calculate it with a tape measure →
Normalized FFMI
0
162532
Fat-free mass
–
FFMI (raw)
–
To 25.0
–
Get the app – track training and body in one place →
FFMI depends heavily on the body fat percentage entered.
Quick answer

FFMI is fat-free mass divided by height squared. In Kouri et al. (1995), the normalized FFMI of athletes who had not used steroids extended up to a limit of 25.0.

What is FFMI?

The fat-free mass index (FFMI) relates fat-free mass to height: fat-free mass in kg ÷ (height in m)². Kouri et al. (1995) added a correction of 6.3 × (1.80 m − height) to normalize values to a height of 1.80 m. Unlike BMI, FFMI distinguishes between muscle and fat mass.

Is there a natural limit?

Kouri et al. (1995) studied 157 male athletes, 83 users and 74 non-users of anabolic-androgenic steroids. The normalized FFMI of the non-users extended up to a well-defined limit of 25.0. Twenty Mr. America winners from the pre-steroid era (1939–1959) had an estimated mean FFMI of 25.4. Many steroid users exceeded 25.0, some even 30.

The authors themselves describe their findings as preliminary. An FFMI above 25 is therefore not proof of steroid use, especially since body fat measurement errors shift FFMI considerably. The study included men only.

Make muscle gain measurable

GymLog AI logs training, meals and weight via chat – no forms, no lists.

Download on the App StoreGet it on Google Play

Related questions

Sources

  1. Kouri, E. M., Pope, H. G. Jr., Katz, D. L. & Oliva, P. (1995). Fat-free mass index in users and nonusers of anabolic-androgenic steroids. Clin J Sport Med, 5(4), 223–228. PubMed
This content is for general informational purposes only and is not a substitute for medical advice. Results from equations are estimates and may vary individually.