Calculate your Fat-Free Mass Index (FFMI) to estimate your muscularity relative to your height, adjusted for a fair comparison across body sizes.
Calculated instantly in your browser — nothing is sent to or stored on our servers.
How This Is Calculated
FFMI (Fat-Free Mass Index) measures how much muscle mass you carry relative to your height — similar to BMI, but using lean mass instead of total weight, which makes it a better gauge of muscularity.
The Formula
Fat-Free Mass (kg) = Weight(kg) × (1 − Body Fat% / 100). FFMI = Fat-Free Mass(kg) ÷ Height(m)². Normalized FFMI = FFMI + 6.1 × (1.8 − Height(m)) — this adjusts for height so taller and shorter people can be fairly compared.
Most adult men without significant muscle-building training fall between 18-20. Values above 25 are rare without years of dedicated training, and very high values may suggest performance-enhancing drug use.
FFMI depends on the quality of your body-fat estimate.
Treat FFMI as a comparison tool, not a diagnosis or a verdict on your physique. Re-check with consistent measurements if you are tracking change over time.
RELATED CALCULATORS