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Ideal Weight (Hamwi Formula) Calculator

See your ideal body weight with the Hamwi formula.

How it is calculated

The Hamwi rule starts from a baseline at 5 feet (152.4 cm) and adds or subtracts a fixed amount for every inch of height above or below it. For men: IBW = 48.0 + 2.7 × n kg. For women: IBW = 45.5 + 2.2 × n kg. Here n = (H − 152.4) ÷ 2.54 is the number of inches over 5 feet and H is height in centimetres. The pound figure is the kilogram value times 2.20462. Any sex value other than female uses the male line. The tool accepts heights from 140 to 272 cm; anything outside that range, or an empty height, shows no result. The rule only uses height, so frame size, age and muscle are ignored, and it was written for adults.

Worked example

A man is 175 cm tall. Height over 152.4 cm is 175 − 152.4 = 22.6 cm, which is 22.6 ÷ 2.54 = 8.90 inches. The extra weight is 2.7 × 8.90 = 24.02 kg. Adding the male baseline gives 48.0 + 24.02 = 72.02 kg. In pounds, 72.02 × 2.20462 gives 158.78 lb. A woman of 165 cm would get 45.5 + 2.2 × 4.96 = 56.41 kg with the female line.

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Common mistakes

  • Entering height in feet or inches. The field is centimetres, so 5.8 is read as a 5.8 cm person and the tool shows no result; the same happens for any height under 140 cm.
  • Using the result for a child or a very short adult. Below 5 feet the formula keeps subtracting, which is why heights under 140 cm are refused rather than given a meaningless weight.
  • Not choosing the sex. Anything other than female takes the male baseline of 48 kg, which is 2.5 kg higher at 5 feet.
  • Treating the figure as a target for everyone. It uses only height, so an athlete with high muscle mass can sit well above it while being healthy.
  • Comparing it with Devine or Robinson results and expecting a match. Each formula has its own baseline and per-inch step.

Sources

About this calculator

The Hamwi formula, published by Dr. George Hamwi in 1964, was one of the earliest widely adopted methods for estimating ideal body weight from height alone, with separate baseline calculations for men and women and an adjustment added or subtracted per inch of height above or below five feet. It predates the BMI-based approach and was originally developed to help clinicians estimate medication dosing weight quickly, at the bedside, without a chart.

Despite its age, the Hamwi formula is still referenced in nutrition and clinical settings today, often alongside newer methods like Devine or Robinson, as a quick reference point for ideal weight. This calculator applies the original 1964 equation to your height and sex to return an ideal-weight estimate, useful as a rough benchmark rather than a precise clinical target.

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