Key facts
- Calculated from lean body mass and height.
- Below 18 is below average; 22–25 is excellent.
- A normalized FFMI above ~25 is rare for drug-free lifters.
- Requires knowing your body-fat percentage.
FFMI was designed to assess muscularity in a way that BMI cannot, because BMI counts fat and muscle the same. By stripping out body fat and looking only at fat-free mass relative to height, FFMI gives a clearer picture of how muscular someone actually is.
To calculate it, you work out your fat-free mass (weight × (1 − body-fat%)), divide by your height in metres squared, and normalize to a standard height. A score below 18 is below average, 18–20 average, 20–22 above average, 22–25 excellent, and above 25 elite.
FFMI is often cited in discussions of the natural muscle-building limit, since drug-free athletes rarely exceed a normalized FFMI of around 25. It is an estimate that depends on an accurate body-fat reading, so pair it with a consistent body-fat measurement method.
Frequently asked questions
What is a good FFMI?
Below 18 is below average, 18–20 is average, 20–22 is above average, 22–25 is excellent, and above 25 is considered elite. Natural lifters rarely exceed a normalized FFMI of about 25.
How is FFMI different from BMI?
BMI uses total body weight and can't tell muscle from fat, so muscular people often register as 'overweight'. FFMI removes fat and measures only lean mass relative to height, making it a better gauge of muscularity.
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