Fat-free mass index calculator
FFMI is lean mass divided by height squared — BMI with the fat taken out. It is the usual way of asking whether a physique is achievable naturally.
%
FFMI
21.73
- Height-adjusted FFMI Normalised to 1.8 m, so tall and short people compare fairly.
- 21.73
- Fat-free mass
- 70.40
Show the working
- Weight = 80
- Height = 180
- Body fat = 12
- h_m = 180 / 100 = 1.8
- Fat-free mass = 80 * (1 - 12/100) = 70.4
- FFMI = 70.4 / 1.8^2 = 21.7284
- Height-adjusted FFMI = 21.7284 + 6.1 * (1.8 - 1.8) = 21.7284
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- FFMI = fat-free mass in kg / (height in m)^2
- adjusted FFMI = FFMI + 6.1 x (1.8 - height in m)
The often-quoted natural ceiling around 25 comes from a 1995 study of pre-steroid-era bodybuilders. It is a statistical observation about one sample, not a law of physiology.
This is a population formula, not a diagnosis. Individual metabolism, body composition and medical history all move the real answer, so treat the number as a starting point and talk to a clinician about anything that matters.