Fat-Free Mass Index (FFMI) Calculator

FFMI is a measure of muscularity that normalizes lean body mass for height, similar to BMI but using lean mass instead of total mass. It is calculated as: FFMI = fat-free mass (kg) / height (m) squared. An adjusted FFMI normalized to 1.8 m height is also commonly used: adjusted FFMI = FFMI + 6.1 x (1.8 - height).

Research by Kouri et al. (1995) published in the New England Journal of Medicine found that natural (non-anabolic-steroid-using) bodybuilders rarely exceed an FFMI of 25. Many researchers and coaches use 25 as an approximate natural upper limit, though some exceptionally well-built natural athletes may slightly exceed it. Values above 26 are rare without performance-enhancing substances.

BMI (body mass index) uses total body weight and does not distinguish between fat and muscle. A muscular athlete may have a high BMI despite very low body fat. FFMI uses only fat-free mass (lean body mass), making it a much better measure of muscularity. Two people with the same height and BMI can have very different FFMI values.

As a rough guide: FFMI under 18 is below average for male lifters, 18 to 20 is average, 20 to 22 is above average, 22 to 24 is well-built, 24 to 25 is near the natural limit for most men, and above 25 is exceptional. For women, natural FFMI values are typically 4 to 6 units lower than for men due to hormonal differences.

You need your total body weight, body fat percentage, and height. FFMI = (body weight x (1 - body fat/100)) / height(m)^2. If you do not know your body fat percentage, you can estimate it using the US Navy circumference method or from skinfold calipers.