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Sep 02, 2026

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FFMI Calculator

Estimate Fat-Free Mass Index from height, weight and body-fat percentage, with an optional height-normalized FFMI value.

Calculate FFMI

FFMI is a body-composition index, not a diagnosis. Consumer body-fat measurements can have meaningful error, so small changes in the result may reflect measurement error rather than a real change in lean mass.

Maintained by Live Fitness Check. Last updated: August 13, 2026. How we test our calculators .

About This Calculator

The FFMI Calculator estimates Fat-Free Mass Index, a body-composition measure that scales fat-free mass to height. Unlike BMI, FFMI requires a body-fat percentage estimate so that body weight can be separated into fat mass and fat-free mass before the index is calculated.

Methodology

Fat-free mass is calculated as body weight × (1 − body-fat percentage). FFMI equals fat-free mass in kilograms divided by height in meters squared. The optional normalized value applies the correction described by Kouri and colleagues: FFMI + 6.3 × (1.80 − height in meters).

Sources

Kouri EM et al. — Fat-free mass index in users and nonusers of anabolic-androgenic steroids: https://pubmed.ncbi.nlm.nih.gov/7496846/
Disclaimer
FFMI depends on the accuracy of the body-fat estimate entered and should not be treated as a diagnostic test or as proof of steroid use, health status or athletic potential. Body-composition methods can produce materially different estimates.

Frequently Asked Questions

What does FFMI measure?

FFMI relates estimated fat-free mass to height, providing a way to compare lean mass across people of different heights.

Why does FFMI require body-fat percentage?

Body-fat percentage is used to estimate fat-free mass before dividing that mass by height squared.

What is normalized FFMI?

It is a height-adjusted version of FFMI using the correction described in the Kouri study to normalize values toward a height of 1.80 meters.

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