Ideal weight calculator
Devine, Robinson, Miller and Hamwi — four formulas that disagree, and why.
Enter a height to see all four formulas.
Where the "ideal weight" formulas come from
There are four of these in common use, they disagree with each other by several kilograms at the same height, and not one of them was built to tell a person what to weigh.
Devine published his in 1974 to calculate gentamicin doses — an antibiotic where the right amount depends on lean mass rather than total weight, and where a clinician needs one number per height without weighing anybody. Hamwi's came from a 1964 American Diabetes Association diet pamphlet. Robinson and Miller both refitted Devine's shape to survey data in 1983. They survive in clinical software because drug dosing genuinely needs a single number per height, not because anyone validated them as health targets.
Formulas
Worked examples
| Height | Devine | Robinson | Miller | Hamwi | Spread |
|---|---|---|---|---|---|
| 5′0″ M | 50 kg | 52 kg | 56.2 kg | 48 kg | 8.2 kg |
| 5′0″ F | 45.5 kg | 49 kg | 53.1 kg | 45.5 kg | 7.6 kg |
| 5′4″ M | 59.2 kg | 59.6 kg | 61.8 kg | 58.8 kg | 3 kg |
| 5′4″ F | 54.7 kg | 55.8 kg | 58.5 kg | 54.3 kg | 4.2 kg |
| 5′8″ M | 68.4 kg | 67.2 kg | 67.5 kg | 69.6 kg | 2.4 kg |
| 5′8″ F | 63.9 kg | 62.6 kg | 64 kg | 63.1 kg | 1.4 kg |
| 5′10″ M | 73 kg | 71 kg | 70.3 kg | 75 kg | 4.7 kg |
| 5′10″ F | 68.5 kg | 66 kg | 66.7 kg | 67.5 kg | 2.5 kg |
| 6′2″ M | 82.2 kg | 78.6 kg | 75.9 kg | 85.8 kg | 9.9 kg |
| 6′2″ F | 77.7 kg | 72.8 kg | 72.1 kg | 76.3 kg | 5.6 kg |
The spread column is the useful one. Four formulas that all claim to give an ideal weight differ by several kilograms at every height.
Worth knowing
- Every one of them is anchored at five feet and adds a fixed amount per inch above it. That shape is the giveaway — it is a dosing nomogram, not a model of a human body.
- None of them takes frame size, build, age or body composition. Two people of the same height get the same answer whatever they are made of, which is the same blind spot BMI has.
- Hamwi was published in pounds — 106 lb plus 6 lb an inch for men, 100 lb plus 5 lb an inch for women. The kilogram constants everyone quotes are a rounded restatement, and they drift: about 0.1 kg at five feet, but 0.8 kg by 5 ft 2 in for women.
- Below five feet all four are pure extrapolation and they diverge sharply. This tool extrapolates rather than clamping, because a clamp would hide the disagreement.
Frequently asked questions
- What is my ideal weight?
- There is no such number, which is why four formulas that all claim to give it disagree by several kilograms. A more useful question is whether your weight is stable, whether your waist is under half your height, and how you feel — none of which a height-only formula can address.
- Why do the four formulas give different answers?
- Because they were fitted for different purposes on different data. Devine chose constants that made gentamicin dosing work; Hamwi's came from a diet pamphlet; Robinson and Miller refitted Devine's shape to 1980s survey data. None was validated against health outcomes, so there is no basis for preferring one.
- Which formula do doctors actually use?
- Devine, overwhelmingly, and almost always for drug dosing rather than weight advice. It is embedded in pharmacy software for calculating doses of drugs that distribute in lean tissue. That is the job it was designed for and the one it does well.
- What if I am shorter than five feet?
- Every one of these formulas is extrapolating below five feet, because that is where their anchor point sits and none of the source populations had many people under it. They diverge sharply there. This tool shows the numbers anyway rather than clamping, so you can see how far apart they get.