Body composition

Calculate FFMI

The fat-free mass index shows how much lean mass you carry for your height. Unlike BMI, it separates muscle from fat.

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How it works

First the calculator works out your lean mass: body weight minus fat mass. It divides this by your height in meters squared, just like BMI.

Taller people get slightly higher values at the same build. Kouri et al. (1995) therefore introduced a normalized FFMI that converts to a height of 1.80 m and makes people of different heights comparable.

How to use your result

In the study by Kouri et al. (1995) on strength athletes, men who did not use anabolic steroids reached a normalized FFMI of up to about 25. That is a guide from one sample, not a fixed limit.

In a Lean Bulk, FFMI shows you whether your gain comes from lean mass: if it rises while body fat percentage stays the same, your build is going well. In a Cut it should stay as stable as possible.

FFMI is only as accurate as your body fat percentage. Even a few percentage points of error shift it noticeably. The study examined men; for women there are no comparably established reference values.

Formula and source

Lean mass (kg) = weight (kg) × (1 - body fat (%) ÷ 100)
FFMI = lean mass (kg) ÷ height (m)²
Normalized FFMI = FFMI + 6.1 × (1.8 - height (m))

Kouri EM, Pope HG Jr, Katz DL, Oliva P (1995): Fat-free mass index in users and nonusers of anabolic-androgenic steroids. Clinical Journal of Sport Medicine 5(4).

Frequently asked questions

That depends on sex, height and training years. More useful than comparing yourself with others is your own trend: a rising FFMI at the same body fat means you are building lean mass.

Taller people mathematically have a slightly higher FFMI at the same build. The correction after Kouri et al. converts to 1.80 m so values can be compared.

No. The value comes from a single sample from 1995 and is a rough guide. Some individuals are above it, and an estimated body fat percentage makes any single value uncertain.

As accurate as your body fat percentage. If the estimate is off by a few percentage points, your FFMI shifts too. So always measure with the same method and watch the trend.

All results are estimates and do not replace advice from a doctor or dietitian.

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