Four equations are in common use, all built as weight from height, and they give different answers for the same person. For a man of 175 cm — which is 68.9 inches, or 8.9 inches over five feet:
| Formula | Year | Rule for men | Result at 175 cm |
|---|---|---|---|
| Hamwi | 1964 | 48 kg + 2.7 kg per inch over 5 ft | 72.0 kg |
| Devine | 1974 | 50 kg + 2.3 kg per inch over 5 ft | 70.5 kg |
| Robinson | 1983 | 52 kg + 1.9 kg per inch over 5 ft | 68.9 kg |
| Miller | 1983 | 56.2 kg + 1.41 kg per inch over 5 ft | 68.8 kg |
A spread of 3.2 kg between formulas that are all called ideal. Now compare that to the healthy BMI range of 18.5 to 24.9, which at 1.75 m spans 56.7 kg to 76.3 kg — a window nearly 20 kg wide. Four different point estimates sitting inside one very broad healthy band is the clearest evidence that the precision implied by these formulas does not exist.
This is the fact that reframes everything. The Devine formula, the most cited of the four, was published in 1974 as a way to calculate drug doses — specifically to scale medications that distribute through lean tissue rather than fat, so that dosing an obese patient by total body weight would not overshoot. It was never validated as a health or aesthetic target. Hamwi came from a diabetes-education context for estimating calorie needs. Their survival as consumer ideal weight tools is an accident of convenience, not evidence.
They are still genuinely useful in clinical practice for ventilator tidal volume settings, chemotherapy dosing and renal function estimates. They are poor guides for what you should weigh.
Every one of these equations takes a single input. Things they cannot see:
If the actual question is health rather than a number on a chart, these are more informative and just as easy to take at home:
Use the figures on this page as a rough orientation point and nothing more. They do not apply to children or adolescents, to pregnant or breastfeeding women, to people with significant muscle mass or amputation, or to anyone with fluid retention from a heart, kidney or liver condition. A healthy weight for you is a conversation with a clinician who can see your body composition, history and blood work. This page is general information, not medical advice, and if weight is a source of anxiety or you have any history of disordered eating, a formula is the wrong tool entirely.
For orientation, none of them individually — look at the range they produce together, and check it against the healthy BMI band. If a clinician has asked you for ideal body weight for a dosing calculation, Devine is the usual convention.
Because average lean mass and body composition differ, the equations shift the baseline down by a few kilograms for women. It is a population average being applied to an individual, with all the imprecision that implies.
Usually not. BMI cannot distinguish muscle from fat, and it misclassifies muscular people routinely. Waist to height ratio is the better check in that situation.
No. Your height and sex are used only in your browser to run the four formulas, and nothing is transmitted or stored.
Every tool comes with a written guide, and every category is one click away.