FFMI Calculator
FFMI—fat-free mass index—relates estimated lean body mass to height. It can help describe muscularity, but it is not a drug test, diagnosis or reliable way to decide whether an individual is “natural.”
FFMI inherits the error of your body-fat estimate. A small body-fat measurement error can noticeably change the result.
Calculate FFMI
How FFMI is calculated
Fat-free mass is estimated from body weight and body-fat percentage. FFMI then divides fat-free mass by height squared. A height-normalized version adjusts the result toward a reference height of 1.8 m.
About the famous “25 FFMI” number
A frequently cited 1995 study found normalized FFMI values up to about 25 among the non-steroid-using male athletes in its sample. That historical observation is useful context, but it should not be converted into a universal biological ceiling or used to accuse an individual of drug use.
Better uses for FFMI
- Track your own long-term body-composition trend when measurements are collected consistently.
- Compare broad muscularity context among people of different heights.
- Pair it with strength, waist measurement, photos and performance rather than treating one number as definitive.