The four formulas disagree by 5.8 kg, and the healthy range is 3.6 times wider than their disagreement. More importantly: Devine was built in 1974 for calculating drug doses, and Hamwi in 1964 for estimating calorie needs in diabetes care. Neither was ever meant to tell a person what to weigh.
Ideal Weight Calculator
LiveThe range is wider than the argument about it
| For a man of 180 cm | Result | Span |
|---|---|---|
| Miller, 1983 | 71.5 kg | The four disagree by 5.8 kg |
| Robinson, 1983 | 72.6 kg | |
| Devine, 1974 | 75.0 kg | |
| Hamwi, 1964 | 77.3 kg | |
| Healthy BMI range | 59.9–80.7 kg | 20.7 kg — 3.6 times wider |
What these formulas were actually built for
| Formula | Original purpose | What that means |
|---|---|---|
| Devine, 1974 | Calculating drug doses | Written for gentamicin dosing. It needed a consistent number for a body, not a healthy one. It is still used clinically for exactly that |
| Hamwi, 1964 | Estimating calorie needs in diabetes care | A clinician’s quick rule for meal planning, published without a supporting study |
| Robinson, 1983 | Revising Devine against data | Fitted to actuarial height and weight tables. An improvement on Devine’s arithmetic, not a different idea |
| Miller, 1983 | Also revising Devine | Same year, different data, different answer — which is itself informative about how settled any of this is |
None of these was designed to tell a person what to weigh. They were clinical shortcuts that escaped into consumer health, where the word “ideal” did work the authors never intended. Devine himself described his rule as arbitrary.
Where the formulas came from, and why they climb so slowly
All four share the same shape: a base weight at 5 feet, plus a fixed amount per inch above it. The differences are entirely in those two constants:
| Formula | Base at 5 ft (male) | Per inch above | Note |
|---|---|---|---|
| Devine | 50.0 kg | 2.3 kg | Round numbers, chosen for ease of mental arithmetic |
| Robinson | 52.0 kg | 1.9 kg | Higher base, slower climb |
| Miller | 56.2 kg | 1.41 kg | The highest base and the slowest climb, so it crosses the others |
| Hamwi | 48.0 kg | 2.7 kg | The steepest. Gives the highest figure for tall people and the lowest for short ones |
Because the climbs differ, the formulas rank differently at different heights. Hamwi is the highest for a tall person and the lowest for a short one. There is no consistent “most generous” formula — which is another way of saying the disagreement is not a small correction to a shared truth.
What a healthy weight range actually depends on
| Factor | In the formulas? | Why it matters |
|---|---|---|
| Height | Yes | The only real input |
| Sex | Yes | A different constant, nothing more |
| Muscle mass | No | Muscle is denser than fat. A trained person can weigh well above any formula and be healthier than someone below it |
| Body composition | No | Where fat sits matters more than how much there is. Waist measurement carries more information than weight |
| Age | No | Some evidence suggests a slightly higher weight is protective in older adults |
| Ethnicity | No | Metabolic risk begins at lower BMI thresholds in South and East Asian populations |
| Fitness | No | Cardiorespiratory fitness predicts health outcomes better than weight in much of the research |
A waist measurement is more informative than any of this and takes ten seconds. Waist-to-height below 0.5 is the widely used screening threshold, it needs no formula and no chart, and it captures something the scale cannot.
Common mistakes
Frequently asked questions
Which ideal weight formula is correct?
None of them, in the sense the question means. They disagree by nearly 6 kg for the same person because they were fitted to different data for different purposes. The healthy BMI range for a given height is 3.6 times wider than their disagreement, and that range is the more honest answer.
Why was the Devine formula created?
For calculating drug doses — specifically gentamicin. It needed a consistent, reproducible figure so that different clinicians arrived at the same dose. It was never proposed as a healthy weight, and it is still used clinically for its original purpose.
Does frame size really change anything?
The conventional adjustment is around 10% either way, and it is a convention rather than a measured relationship. Frame is usually estimated from wrist circumference or elbow breadth, and the evidence linking it to a healthy weight is weak. It is offered above because people expect it, not because it adds much.
What should I use instead?
A waist measurement, which takes ten seconds and needs no formula. Waist-to-height below 0.5 is the common screening threshold, and it captures where fat sits — which carries more information about health than total weight does. For anything beyond screening, a doctor.
Do these formulas work for athletes?
No. They use height and sex and nothing else, so they cannot distinguish muscle from fat. A trained person routinely weighs above every formula while being in better health than someone below all of them. The same limitation applies to BMI.
Are the thresholds the same for everyone?
No. Metabolic risk begins at lower BMI values in South and East Asian populations, which is why several health systems use lower thresholds for those groups. The formulas above make no such distinction, because they were fitted to mid-century North American data.
Why do the formulas rank differently at different heights?
Because they differ in both the base weight and the amount added per inch. Hamwi has the lowest base and the steepest climb, so it gives the lowest figure for short people and the highest for tall ones. There is no formula that is consistently higher than the others.
Is anything I enter sent anywhere?
No. Everything runs in your browser with no server request, and works offline once the page has loaded. Nothing is written to disk and nothing persists after you close the tab — which matters more than usual for a page like this one.
Sources
- Devine BJ. “Gentamicin therapy.” Drug Intelligence and Clinical Pharmacy, 1974;8:650–655. The original formula, published for antibiotic dosing rather than for assessing health.
- Robinson JD, Lupkiewicz SM, Palenik L, et al. “Determination of ideal body weight for drug dosage calculations.” American Journal of Hospital Pharmacy, 1983;40(6):1016–1019.
- Miller DR, Carlson JD, Loyd BJ, Day BJ. “Determining ideal body weight.” American Journal of Hospital Pharmacy, 1983;40(10):1622.
- Hamwi GJ. “Therapy: changing dietary concepts.” In: Diabetes Mellitus: Diagnosis and Treatment. American Diabetes Association, 1964:73–78.
- World Health Organization. The 18.5–24.9 healthy BMI band used for the range above, and the lower thresholds applied in Asian populations.
- Ashwell M, Gunn P, Gibson S. “Waist-to-height ratio is a better screening tool than waist circumference and BMI.” Obesity Reviews, 2012;13(3):275–286. The basis for the 0.5 threshold.
Every figure on this page is computed from the published formulas rather than quoted, so the article and the calculator cannot disagree. Nobody involved in producing this page is a clinician — and the strongest thing this page can tell you is that the number it produces was never meant to be a target.
Related calculators
See the full list of Health calculators, or try:
- Waist-to-Height Ratio — more informative, and faster
- BMI Calculator — eight scales including Asian thresholds
- Body Fat Calculator — what the weight is made of
- FFMI Calculator — lean mass adjusted for height
- Waist-Hip Ratio — where the fat sits
- BMR Calculator — how the equations were built