How this calculator works
Fat-free mass divided by height squared gives adult FFMI. You may supply a body fat estimate or use Boer's adult lean mass equation. This page uses the sheet's conventional 6.1 height correction to a 1.8 m reference; Kouri's original abstract reports 6.3. Athlete benchmarks came from male samples and are not universal limits or proof of steroid use. Pregnancy, oedema and unusual body composition limit these estimates. The result is an estimate for information only and is not medical advice.
Formula
FFM = weight x (1 - body fat fraction), or Boer LBM. FFMI = FFM / height². Height-adjusted FFMI = FFMI + 6.1 x (1.8 - height), with kg and metres.
Worked example
At 80 kg, 15% body fat and 1.80 m, FFM is 68 kg and FFMI is 21.0. Boer at 80 kg and 175 cm gives 60.085 kg, FFMI 19.6 and height-adjusted FFMI 19.9.
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Frequently asked questions
Is an FFMI of 25 a hard natural limit?
No. The often quoted value comes from a small male athlete study and is not an individual diagnostic boundary.
Why do the two methods differ?
Body fat estimates and the Boer height-weight prediction have different errors. Neither is a direct body composition measurement.
Why is the height-adjusted value different?
FFMI tends to be lower at greater heights, so the adjustment adds 6.1 times (1.8 minus height in metres) to make comparisons across heights less biased.