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Your fat-free mass index

Evaluates muscle development relative to height.

ft
in
lb
in
in
in
FFMIVery good
17.3
height-adjusted · raw FFMI 16.6
Lean mass
103.1 lb
Body fat
26.9 %
FFMI evaluates your lean body mass independently of height. The label above is the category matching your height-adjusted value.

What is FFMI?

FFMI (fat-free mass index) evaluates your lean body mass relative to your height and offers a practical reference for tracking muscle development; think of it as a lean-mass-focused version of BMI. BMI looks at total weight, while FFMI considers only lean mass. Lean mass includes not just muscle but also water, bone and other fat-free tissue.

This lets muscle development be judged independently of height, so people of different heights can be compared fairly. The ranges differ by sex; for women they are lower than for men.

Since the value is based on lean mass, its accuracy depends on the body fat percentage you enter; treat the result as an estimate.

How is it calculated?

FFMI shows the level of muscle and other lean tissue relative to height. BMI considers total weight, while FFMI considers only lean mass.

The calculation has two steps. First lean mass is found from body fat percentage, then that value is divided by the square of height:

Lean mass = weight × (1 − body fat / 100)
FFMI = lean mass / height²

Weight is in kilograms and height in metres.

Calxin also provides a height-adjusted FFMI, which balances the difference between tall and short people for a more consistent comparison:

Adjusted FFMI = FFMI + 6.3 × (1.8 − height)

Categories by height-adjusted FFMI:

CategoryMaleFemale
Low< 18< 13
Normal18 – 2013 – 15
Athletic20 – 2215 – 17
Very good22 – 2317 – 19
Superior23 – 2619 – 21.5
Exceptional≥ 26≥ 21.5

These ranges are guidance, not strict limits. An adjusted FFMI around 25 is a reference commonly used in natural bodybuilding assessments; it is not a strict biological limit, and some athletes exceed it.