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Broca Index Ideal Weight Calculator

Get the Broca index ideal weight from your height, with the 10% (men) and 15% (women) correction applied.

How it is calculated

The tool subtracts 100 from your height in centimetres to get the original Broca figure, then applies the modified index: ideal = (height − 100) × 0.90 for men and ideal = (height − 100) × 0.85 for women. It shows three numbers: the corrected ideal weight in kilograms, the uncorrected original figure, and the ideal weight in pounds (kg × 2.20462). Height is the only measurement used; age, frame size, muscle mass and body fat do not enter the formula. Height must be above 100 cm and no more than 272 cm, and it must be tall enough that the result is a real body weight (at least 2 kg): 102 cm gives no result, 103 cm does. A missing or unrecognised sex value is treated as male. The result is a single reference value, not a healthy range.

Worked example

A woman is 165 cm tall. Base figure = 165 − 100 = 65 kg, which is the original Broca value. Women get a 15% reduction: 65 × 0.85 = 55.25 kg. In pounds that is 55.25 × 2.20462 = 121.81 lb. A man of the same height would get 65 × 0.90 = 58.50 kg, which shows how much the sex correction alone moves the answer.

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Common mistakes

  • Entering height in metres or feet; the field takes centimetres, and 100 or below (or above 272) gives no result.
  • Treating the single figure as a target weight for athletes or very muscular people, since the formula ignores muscle and frame size.
  • Using it for children and teenagers, or for very tall and very short adults, where the straight-line rule drifts away from other formulas.
  • Comparing it directly with Devine, Hamwi or BMI-based results: each method uses different constants, so they will not agree.
  • Confusing the uncorrected original figure with the final ideal weight; the corrected value is the first one shown.

Sources

About this calculator

The Broca index, devised by 19th-century French surgeon Paul Broca, is one of the oldest formulas for estimating ideal body weight: start with height in centimetres minus 100, then apply a sex-based correction to that base figure — subtracting about 10% for men and about 15% for women reflects the average difference in body frame and composition between the sexes. A 175 cm man, for instance, starts from a base of 75 kg and lands around 67.5 kg after the correction.

Despite predating modern body-composition science by over a century, the Broca index remains popular for its simplicity — no scale, calipers or calculator beyond basic arithmetic are needed — and it is still referenced in some European clinical contexts alongside newer methods like BMI and the Hamwi or Devine formulas, though it does not account for frame size, muscle mass or age the way more modern indices attempt to.

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