FFMI calculator.

How FFMI is worked out

1. Lean mass: body weight × (1 − body fat %).
2. FFMI: lean mass (kg) ÷ height (m) squared.
3. Normalized FFMI: FFMI + 6.1 × (1.8 − height in metres). This adjusts to a 1.8 m (5 ft 11 in) reference height so tall and short people can be compared.

Worked example. 80 kg, 180 cm, 15% body fat: lean mass 68 kg, FFMI 68 ÷ 1.8² = 20.99, normalized FFMI 20.99 (height equals the reference).

What it can and cannot tell you. In Kouri et al.’s 1995 study of male athletes, those who did not use anabolic steroids had normalized FFMI at or below about 25, and some steroid users were above it. That is one sample, not a rule or a test, and the study did not include women. FFMI does not diagnose anything. Body fat estimates can be off by several percentage points, which moves FFMI by about 1 point.

Source (opened 2026-10-04): Kouri EM, Pope HG Jr, Katz DL, Oliva P. Fat-free mass index in users and nonusers of anabolic-androgenic steroids. Clin J Sport Med 1995;5(4):223-228.

FAQ

What is FFMI?

Fat-free mass index is your fat-free (lean) mass in kilograms divided by your height in metres squared. It is like BMI but ignores fat mass.

What is normalized FFMI?

It adds 6.1 times the difference between 1.8 m and your height, so that people of different heights can be compared to a 1.8 m reference.

What is a good FFMI?

There is no official good or bad value. Kouri 1995 reported that non-steroid-using male athletes in their sample were at or below about 25 normalized. Many healthy people are well below that.

Does FFMI prove someone is natural?

No. It was an observation in one study sample and genetics, measurement error and training history all vary. Do not use it as a test.

Can women use this?

The formula works for anyone, but the 1995 reference sample was men, so the 25 mark does not apply to women.