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Body fat percentage from BMI calculator

Deurenberg fitted body fat against BMI, age and sex. It needs nothing but a scale and a tape for height.

years
Body fat
18.13%
= Exact Body fat from BMI
BMI
22.86 kg/m2
Fat mass
12.69
Lean mass
57.31
Show the working
  1. Weight = 70
  2. Height = 175
  3. Age = 30
  4. Sex = 1
  5. BMI = 70 / (175/100)^2 = 22.8571
  6. Body fat = 1.20 * 22.8571 + 0.23 * 30 - 10.8 * 1 - 5.4 = 18.1286
  7. Fat mass = 70 * 18.1286 / 100 = 12.69
  8. Lean mass = 70 - 12.69 = 57.31

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

    • %fat = 1.20 x BMI + 0.23 x age - 10.8 x sex - 5.4, with sex = 1 for men and 0 for women

    Because it is built on BMI, it inherits every one of BMI limitations: it will call a lean, muscular person fat.

    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.

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