Ideal Weight Calculator

Enter a height in centimetres or feet and inches, pick male or female, and see what the four classical formulas — Devine, Robinson, Miller and Hamwi — each return, next to the weight range that corresponds to a BMI of 18.5 to 24.9 for that height.

All four have the same shape: a base weight at exactly five feet, plus a fixed number of kilograms for every inch above it. That shape is the first thing to notice, because it means they only behave sensibly near the height they were fitted to. At 175 cm the four answers for a man are 70.5, 68.9, 68.7 and 72.0 kg — a spread of 3.3 kg, close enough that picking one hardly matters. At 190 cm they read 84.0, 80.1, 77.1 and 88.0, a spread of 10.9 kg. At 120 cm the linear term has gone deeply negative and they give 20.7, 27.8, 38.2 and 13.6 kg, with Hamwi's answer falling well below the 26.6 kg that a BMI of 18.5 would put as the lower bound. A formula that disagrees with itself by a factor of nearly three is not measuring anything.

It is worth knowing where these came from. Devine's formula was published in 1974 to help calculate drug doses, not to set a healthy weight; Robinson's and Miller's are later regressions on similar data. None of them was derived as a health target, none accounts for build, muscle or body composition, and none distinguishes a heavy athlete from a heavy anything else.

Which is why the BMI band is shown beside them. At 175 cm it runs 56.7 to 76.3 kg, a range of nearly 20 kg that contains all four formula answers comfortably — a fair picture of how much latitude there actually is, and a reminder that a single number labelled "ideal" is the least useful thing on this page.