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Health Calculators

Fat Free Mass Index Calculator

Verified formula Updated Jun 2026 Private — runs on your device

Enter details
kg
%
cm
Verified formula Private

Fat-free mass index (FFMI)

19.43

Fat-free mass
59.50

For general information only — not financial, tax, legal or medical advice. Verify before you rely on it.

How to use the Fat Free Mass Index Calculator

The Fat Free Mass Index Calculator works out your fat-free mass index (ffmi), along with 1 related figure in an instant. Enter weight, body fat percentage and height and the result updates as you type — it is free, needs no sign-up, and runs entirely in your browser so your figures stay private.

  1. Enter the weight.
  2. Enter the body fat percentage.
  3. Enter the height.
  4. Read off your fat-free mass index (ffmi), together with fat-free mass — the calculator updates automatically, with no button to press.

Formula

The Fat Free Mass Index Calculator uses the formula:

Fat-free mass index (FFMI) = (Weight × (1 - Body fat percentage ÷ 100)) ÷ ((Height ÷ 100) ^ 2)

Worked example

For example, with weight of 70 kg, body fat percentage of 15% and height of 175 cm, the fat-free mass index (ffmi) is 19.43.

Inputs used
Weight 70 kg
Body fat percentage 15%
Height 175 cm
Results
Fat-free mass index (FFMI) 19.43
Fat-free mass 59.50

Results are estimates for educational use, not professional advice.

Key terms explained

Percentage
A number expressed as a fraction of 100, written with the % sign.
Body fat
The proportion of your body weight that is fat, as opposed to muscle, bone and water.

Frequently asked questions

Fat-free mass index measures lean mass relative to height, similar to BMI but using only fat-free weight. It indicates muscularity rather than overall weight.

First find fat-free mass = weight × (1 − body fat %). Then divide by height in metres squared. For 70 kg at 15% fat and 1.75 m, FFMI is about 19.4.

For men, roughly 18–20 is average and around 25 is near the natural muscular limit. Women's values are generally a few points lower.

BMI can label muscular people as overweight. FFMI separates muscle from fat, giving a fairer view of a lean, muscular build.

Enter the weight. Enter the body fat percentage. Enter the height. Read off your fat-free mass index (ffmi), together with fat-free mass — the calculator updates automatically, with no button to press.

Body Composition: Looking Beyond the Scale

Why the number on the scale tells only part of the story — body fat, lean mass, the FFMI, where fat is stored, and how to measure and track your true body composition.

3 min read

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