Ideal Body Weight Calculator

Calculator

How we calculate it

Four ideal body weight equations are in common use and all share the same shape: a base weight at five feet plus an increment for every inch above that. Devine (1974) uses 50.0 kg for men and 45.5 kg for women plus 2.3 kg per inch. Robinson (1983) uses 52.0 kg and 49.0 kg with 1.9 kg and 1.7 kg per inch. Miller (1983) uses 56.2 kg and 53.1 kg with 1.41 kg and 1.36 kg per inch. Hamwi (1964) was published in pounds — 106 lb plus 6 lb per inch for men and 100 lb plus 5 lb per inch for women — and is applied here in that original form and converted, rather than using one of the several incompatible rounded metric restatements in circulation. Adjusted body weight, which some dosing calculations use when actual weight is well above ideal, is reported as ideal body weight plus 0.4 times the difference. The weight range corresponding to a BMI of 18.5 to 24.9 is shown alongside, because that WHO range is usually what people mean by a healthy weight, and because it is a range rather than a single number. The historical review by Pai and Paloucek traces all four equations to drug-dosing practice rather than to any research into which weight is healthiest, and notes that Devine published only a male equation — the female form in universal use was a later convention.

Important limitations

• These are not health targets. All four equations were written to size drug doses — Devine’s came from a gentamicin dosing paper — and none was derived from evidence about which weight is healthiest at a given height.
• The four equations disagree, often by five kilograms or more at the same height, because each was a different author’s adjustment to an earlier rule of thumb rather than a new measurement study.
• Each equation is defined from a base weight at five feet upward. Below that height they are being extrapolated backward, which the original papers did not intend.
• Devine published only a male equation. The female form in universal use was a later convention rather than part of the original paper, though it is the version clinical references apply.
• None of the equations accounts for frame size, muscle mass, age or ethnicity, and none is validated for children, during pregnancy, or after limb amputation.
• The BMI-derived range shown alongside is a population screening range from the WHO adult classification, not a personal target either.