Ideal Weight Calculator

Three formulas, three different answers, and the gap between them is the most informative thing on the screen. This page runs Devine (1974), Robinson (1983) and Miller (1983) side by side and reports how far apart they land, because a single figure presented alone implies a precision that none of them possesses.

What the three equations actually say

All three are straight lines anchored at five feet (152.4 cm), differing only in the starting weight and the kilograms added per inch above it:

                 base (male / female)    per inch over 5 ft (male / female)
Devine   (1974)   50.0 / 45.5 kg          2.30 / 2.30 kg
Robinson (1983)   52.0 / 49.0 kg          1.90 / 1.70 kg
Miller   (1983)   56.2 / 53.1 kg          1.41 / 1.36 kg

Height entered in centimetres is converted to inches internally. A man of 190 cm is 74.8 inches, so 14.8 inches over the anchor. Devine gives 50.0 + 2.30 x 14.8 = 84.0 kg. Robinson gives 52.0 + 1.90 x 14.8 = 80.1 kg. Miller gives 56.2 + 1.41 x 14.8 = 77.1 kg. Nearly seven kilograms separate the highest from the lowest, for the same man on the same day.

At 165 cm the ordering flips: a woman of that height gets 56.9 kg from Devine, 57.4 kg from Robinson and 59.8 kg from Miller. The formulas cross over because their slopes differ, so which one flatters you depends entirely on your height.

These are drug-dosing equations

Devine's formula was not designed to give anyone a weight goal. It appeared in the clinical pharmacy literature as a way to dose gentamicin, and it survives because dosing several classes of drug on total body weight overdoses heavier patients. Creatinine clearance estimated by the Cockcroft-Gault equation uses ideal body weight for the same reason: clearance tracks lean tissue, not total mass. Robinson and Miller were later attempts to fit the same relationship to different reference data.

None of them was validated as a health target, and none of them was derived from outcome data about who lives longer at what weight. Reading a dosing constant as a personal goal is a category error, however widely it is done.

Three things the formulas cannot see

They take height and a binary sex and nothing else. Frame size is invisible: two men of 190 cm, one narrow-boned and one broad, get the same 84.0 kg from Devine. Muscle is invisible, so a trained athlete will sit well above every line without carrying excess fat — the body fat calculator responds to composition in a way these equations cannot. Age is invisible, though body composition changes substantially across adult life.

Below five feet the lines are extrapolating past the data they were fitted to, and the results become unreliable rather than merely imprecise. The calculator flags this rather than pretending otherwise, and refuses to return a value where the arithmetic produces something meaningless.

How to read the output

Treat the spread as the margin. If three published equations disagree by seven kilograms at your height, no number within that range has a claim to being your correct weight. A previous version of this page invented a "Devine plus or minus 10% recommended range" and presented it as though it came from the literature. It did not, and it has been removed rather than re-sourced.

If you want a range that is at least derived from population health data, the healthy-weight band shown by the BMI calculator is a better starting point, and it is wider than most people expect. Other measurement and conversion utilities live under converters if you simply need to move between units.

All three formulas are evaluated in your browser and nothing is transmitted; your entries may persist in your own browser between visits. Nobody with clinical training has reviewed this page, and a target weight worth acting on should come from someone who has met you.