Ideal weight calculator

The ideal body weight formulas

IBW = base weight + increment × i (i = (height in cm − 152.4) ÷ 2.54, i.e. inches over 5 feet)

All three formulas share the same shape: a base weight at 152.4 cm (5 feet) plus a fixed increment for every inch above that. Devine (1974) uses 50.0 kg + 2.3 kg/inch for men and 45.5 kg + 2.3 kg/inch for women. Robinson (1983) uses 52.0 kg + 1.9 kg/inch for men and 49.0 kg + 1.7 kg/inch for women. Hamwi (1964) uses 48.0 kg + 2.7 kg/inch for men and 45.5 kg + 2.2 kg/inch for women.

They were never designed as health targets — they are clinical tools, originally used for drug dosing in patients whose actual weight is a poor basis for a dose (Pai and Paloucek, 2000, on the origin of the "ideal" body weight equations). Two of the three come with a caveat: the coefficients 52/1.9 and 49/1.7 are the conventional rounded form of Robinson's regression, while his paper itself gives 51.65 + 1.85 for men and 48.67 + 1.65 for women; and Hamwi's rule was originally stated in pounds (106 lb + 6 lb per inch for men, 100 lb + 5 lb per inch for women), so the kilogram values are a conventional conversion.

Example: a man 180 cm tall. Inches over 5 feet = (180 − 152.4) ÷ 2.54 = 10.87. Devine gives 50.0 + 2.3 × 10.87 = 75.0 kg, Robinson 52.0 + 1.9 × 10.87 = 72.6 kg and Hamwi 48.0 + 2.7 × 10.87 = 77.3 kg — a range of 72.6 to 77.3 kg.

Why a range beats a single number

For the same height the three formulas differ by several kilograms — not an error, but a consequence of how they were built: different decades, different sources (life-insurance height-weight tables, clinical regressions) and different purposes. None is "more correct" than the others, so showing them together as a range is the honest presentation.

The more practical reference is the WHO healthy weight range, derived from the BMI cut-offs 18.5 and 24.9 multiplied by height in metres squared. For 180 cm that is 59.9 to 80.7 kg — far wider than the formulas' spread, and all three example values fall inside it. If you are choosing a target, the WHO range is the more meaningful one; the formulas are useful only as a rough reference point.

Limitations

The formulas apply to adults (18+). They are defined as an increment "per inch over 5 feet", so below roughly 152 cm they merely extrapolate backwards — and the result can then fall below the WHO healthy range, which makes it useless as a target. The calculator flags that case explicitly.

None of the formulas accounts for frame size, muscle mass, age or fat distribution. A very muscular person can weigh more than their "ideal" weight and be perfectly healthy, while someone inside the range can still carry too much body fat. This calculator is informational and not medical or nutritional advice — for a real assessment of body composition, see a doctor or dietitian.