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FFMI calculator (fat-free mass index)

Short answer

Fat-free mass index is your lean mass in kilograms divided by your height in metres squared, a BMI that ignores fat. Kouri et al. adjusted it to a 1.8 m man by adding 6.3 × (1.80 − height). At 180 cm, 85 kg and 15% body fat, FFMI is 22.3. In their study, athletes who had never used steroids topped out at a height-adjusted FFMI of about 25.

Last reviewed 27 October 20262 published sourcesNot medical advice

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FFMI calculator

Fat-free mass index needs your body fat percentage. Estimate it with the Navy tape method if you don't have a scan.

Units
cm
kg
%

Enter your height, weight and body fat to see your FFMI.

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How FFMI is calculated

First take lean mass: weight × (1 − body fat ÷ 100). FFMI = lean mass (kg) ÷ height (m)². So that people of different heights can be compared, Kouri et al. added 6.3 × (1.80 − height in m) to normalise every result to a 1.8 m man (Kouri et al., 1995).

Worked example: 85 kg at 15% fat is 72.25 kg lean. Divided by 1.80² that is 22.3, and at exactly 1.80 m the height adjustment is zero.

Height-adjusted FFMI by lean mass and height
Height60 kg lean70 kg lean80 kg lean
165 cm23.026.730.3
170 cm21.424.928.3
175 cm19.923.226.4
180 cm18.521.624.7
185 cm17.220.123.1
190 cm16.018.821.5
Lean mass ÷ height² + 6.3 × (1.80 − height), from Kouri et al. (1995).

Body fat is the weak link

FFMI is only as good as the body fat figure behind it. A tape estimate such as the US Navy method (Hodgdon & Beckett, 1984 (men)) is fine for tracking, but an error of a few points in body fat moves FFMI noticeably. Get yours from the body fat calculator, or see lean mass on its own with the lean body mass calculator.

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Common questions

What is a good FFMI?

There is no clinical scale. Kouri et al. reported that in 74 male athletes who had never used anabolic steroids, height-adjusted FFMI reached a well-defined limit of 25.0, and 20 Mr. America winners from before the steroid era averaged 25.4.

Does an FFMI over 25 mean someone uses steroids?

No. Kouri et al. called their findings preliminary and suggested FFMI only as an initial screen. An underestimated body fat figure also inflates FFMI, so a single number proves nothing.

Does FFMI work for women?

The 25 limit came from men. The formula works for anyone, but there is no equivalent published limit for women from that study, so compare your own FFMI over time instead.

Sources

Figures on this page were checked against these publications on 27 October 2026.

  1. Kouri EM, Pope HG Jr, Katz DL, Oliva P. Fat-free mass index in users and nonusers of anabolic-androgenic steroids. Clinical Journal of Sport Medicine. 1995;5(4):223–228. doi.org/10.1097/00042752-199510000-00003
  2. Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men from body circumferences and height. Naval Health Research Center, San Diego, CA; 1984. Defense Technical Information Center report ADA143890. doi.org/10.21236/ADA143890

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