Online Body Fat % and Fat-Free Mass Index Calculators

This is a body fat % calculator based on the US Navy’s formula. It’s very easy to use and seems to be pretty accurate.

After you’ve calculated your body fat %, you can calculate your fat-free mass index (FFMI) using the calculator below. FFMI measures how much muscle you have.

You can look at the FFMI charts on the webpage to see how you compare to the general population. Men and women have different charts. For women, ignore the “FFMI Interpretation” for your number because that is based on men’s charts.

Note that normalized FFMI adjusts FFMI to a height of 180cm (~5’11") so that people with different heights can be compared.

This section applies to women:

The calculator above adjusts women’s FFMI to 5’11" whereas the website below adjusts to 5’4". The normalized FFMI to 5’11" is slightly higher than normalized to 5’4". I’m not sure which one is the right one for women.

The calculator below is the only one I found that adjusts women to 5’4". All other websites (that I’ve seen) adjust both men and women to 5’11".


This calculator puts my BF% at 11%, my bodyscale puts me at 14,2%… I know both methods are in a way approximations but still there is huge difference (2 kg of BF mass to be precise)… but hey, I take 11% from US Navy gladly :sweat_smile:


Fwiw, I think it matches my biometric scale pretty closely. I got 78.5 pounds calculated lean mass as compared to 78.2 pounds muscle mass and 83.2 pounds fat free body weight per my biometric scale. I’m 109 total pounds and apparently plain old average. I guess I’ll take it and be grateful although probably like most people I’d like to be in a little better shape. :slight_smile:


According to Peter Attia’s recent AMA, his FFMI (not sure if normalized) was 23.3 at the end of 2022. That’s higher than 95th percentile - very impressive.