FFMI calculator (fat-free mass index)
FFMI works like BMI but leaves fat out, which is why people who lift use it to track muscle.
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How to use it
- Enter weight, height and body fat.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Lean mass = weight × (1 − fat % ÷ 100). FFMI = lean mass ÷ height (m) squared. Adjusted = FFMI + 6.1 × (1.8 − height in m) (Kouri 1995).
Example
Inputs: Weight = 80 kg, Height = 180 cm, Body fat = 15 %. Result: Adjusted FFMI: 21; FFMI: 21; Fat-free mass: 68 kg.
Limits and caveats
- It depends on the body fat figure you enter, and any error there carries over.
- The often quoted 25 limit comes from a study of male athletes and does not transfer to women as is.
Questions about this tool
What is a normal FFMI?
Untrained men usually sit around 17 to 20 and women around 14 to 17.
Why is there an adjusted FFMI?
Taller people tend to score lower, so Kouri normalised the value to a height of 1.8 m for fair comparison.
What does an FFMI above 25 mean?
The 1995 Kouri study found that level rare among men who had not used steroids.