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Ideal Weight (Robinson Formula) Calculator

See your ideal body weight with the Robinson formula.

How it is calculated

Height is entered in centimetres. The tool converts the excess over 152.4 cm (5 ft) to inches: x = (height − 152.4) ÷ 2.54. For men it then returns 52 + 1.9 × x kilograms, for women 49 + 1.7 × x. The pounds figure is the kilogram value multiplied by 2.20462. Both are shown to two decimals. For a height under 152.4 cm, x is negative and the formula simply subtracts, so shorter people get a lower base; there is no minimum height other than that the final weight must stay positive. Any sex value other than 'female' is treated as male. The result is a single reference figure, not a healthy range, and it ignores age, frame and muscle mass.

Worked example

A man 175 cm tall is 175 − 152.4 = 22.6 cm above the 5 ft base. In inches that is 22.6 ÷ 2.54 = 8.898. Multiply by 1.9 to get 16.91 kg and add the starting 52 kg, giving 68.91 kg. In pounds, 68.906 × 2.20462 gives 151.91 lb. For a woman 165 cm tall the same steps give 49 + 1.7 × 4.961 = 57.43 kg, or 126.62 lb.

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Common mistakes

  • Entering height in feet, inches or metres. The field expects centimetres, so 1.75 or 5.9 gives a meaningless weight.
  • Leaving the sex on the default when calculating for a woman. The male constants give a result that is roughly 4 to 5 kg higher at heights of 165 to 175 cm.
  • Treating the figure as a target for everyone. It is a clinical reference value; muscular builds and different frames can be healthy well above or below it.
  • Comparing the result across formulas without checking the formula name. Devine, Hamwi, Miller and Robinson give slightly different values for the same height.
  • Using the result for children, who are not covered by this adult height-based formula.

Sources

About this calculator

The Robinson formula (1983) is one of several height-based ideal body weight equations used in clinical medicine, calculated separately for men and women from height above a base of 5 feet, with a fixed starting weight plus a per-inch increment added for each inch over that base height (e.g., roughly 52 kg + 1.9 kg per inch over 5 feet for men, with different constants for women). It's one of a family of similar formulas including Devine, Hamwi, and Miller, all developed mid-20th century primarily to standardize drug dosing calculations, not as a general fitness or beauty benchmark.

Clinicians and pharmacists still use Robinson and its sibling formulas today to estimate an ideal body weight for dosing certain medications by weight, and in some clinical nutrition calculations, though these formulas are population averages and don't account for individual differences in frame size, muscle mass, or body composition.

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