What does FFMI describe?
FFMI is fat-free mass divided by height squared. Unlike BMI, it excludes estimated fat mass, but it still includes water, bone, and organs rather than isolating muscle.
FFMI and height normalization
The calculator first subtracts estimated fat mass, then divides by height in metres squared. It also shows the commonly cited height-normalization equation from Kouri and colleagues, referenced to 1.80 m.
How to use this calculator
- 1Enter height, weight, and your body-fat percentage estimate.
- 2Calculate raw and height-normalized FFMI.
- 3Compare like-for-like methods and consistent measurement conditions over time.
Understanding your result
Use FFMI as a descriptive index. The normalized figure is based on a particular research sample and is not a universal adjustment for every body type. No single FFMI value can establish drug use, a genetic ceiling, or health status.
Assumptions & limitations
- Body-fat input error and changes in hydration can materially change FFMI.
- Published athlete reference values are not diagnostic cutoffs for the general population.
Frequently asked questions
How is FFMI different from BMI?+
BMI uses total body weight. FFMI uses estimated fat-free mass, so it requires a body-fat input and carries that input's uncertainty.
Why show a normalized FFMI?+
The adjustment attempts to reduce the relationship between height and FFMI using a 1.80 m reference. It is one research-derived convention, not a perfect correction.
Does an FFMI above 25 prove steroid use?+
No. A population observation cannot establish an individual's drug use or a universal natural limit. Measurement error and body variation matter.
Will losing fat always change my FFMI?+
If true fat-free mass and height remain unchanged, FFMI remains unchanged. Estimated FFMI may still move because the measurements contain error.
