How to Calculate Your Ideal Weight (Devine, Robinson, Miller, Hamwi)
Ideal body weight is a single number derived from your height and sex, using one of four formulas doctors and dietitians have relied on since the mid-20th century. A man who is 175 cm tall averages 70.0 kg across all four. The calculator below runs the same math on your own numbers.
How the four formulas work
Each formula anchors at 5 feet (152.4 cm) and adds a fixed weight for every inch above that height. The anchor and the per-inch slope differ by formula and by sex, which is why the same height produces four slightly different answers rather than one.
Nobody uses just one of these today because none of them was built from a large enough or diverse enough sample to be treated as definitive. Devine came out of a 1974 paper meant to standardize drug dosing, not to define a health target. Robinson and Miller followed a few years later as refinements of the same idea. Hamwi is older still, a rule of thumb from 1964 that clinicians used before calculators made the arithmetic trivial. Running all four and averaging them smooths out the quirks of any single formula.
None of the four accounts for how that weight is made up. Bone density, muscle mass and where a person carries fat don’t enter the equation at all, only height and sex do.
The four formulas
Let x equal the number of inches of height above 5 feet: x = height in cm / 2.54 minus 60.
Men
| Formula | Equation |
|---|---|
| Devine | 50 + 2.3x |
| Robinson | 52 + 1.9x |
| Miller | 56.2 + 1.41x |
| Hamwi | 48 + 2.7x |
Women
| Formula | Equation |
|---|---|
| Devine | 45.5 + 2.3x |
| Robinson | 49 + 1.7x |
| Miller | 53.1 + 1.36x |
| Hamwi | 45.5 + 2.2x |
All four results come out in kilograms. Notice that the per-inch slope for men and women is close within each formula, Devine uses 2.3 for both sexes, but the starting weight at 5 feet is always lower for women. That’s where the male/female gap comes from, not from a different growth rate per inch.
Worked example: man, 175 cm
First, find x: 175 / 2.54 minus 60 = 8.9.
| Formula | Calculation | Result |
|---|---|---|
| Devine | 50 + (2.3 x 8.9) | 70.5 kg |
| Robinson | 52 + (1.9 x 8.9) | 68.9 kg |
| Miller | 56.2 + (1.41 x 8.9) | 68.7 kg |
| Hamwi | 48 + (2.7 x 8.9) | 72.0 kg |
| Average | (70.5 + 68.9 + 68.7 + 72.0) / 4 | 70.0 kg (154.3 lb) |
The four estimates spread across a 3.3 kg band, from 68.7 to 72.0 kg, with Hamwi giving the heaviest number and Miller the lightest. That spread is normal. It’s also why the tool shows all four rather than presenting a single figure as the answer.
Reference table by height
Average of all four formulas, men and women, from 150 to 190 cm in 5 cm steps:
| Height (cm) | Men avg (kg) | Women avg (kg) |
|---|---|---|
| 150 | 49.6 | 46.5 |
| 155 | 53.7 | 50.2 |
| 160 | 57.8 | 53.9 |
| 165 | 61.9 | 57.7 |
| 170 | 65.9 | 61.4 |
| 175 | 70.0 | 65.1 |
| 180 | 74.1 | 68.8 |
| 185 | 78.2 | 72.5 |
| 190 | 82.3 | 76.3 |
Each 5 cm step adds roughly 4 kg for men and 3.7 kg for women. The gap between the two columns holds fairly steady too, around 4 to 6 kg at every height in the table, which is the combined effect of the lower base weight and slightly different slopes in the female versions of each formula.
Worked example: woman, 165 cm
x = 165 / 2.54 minus 60 = 5.0.
| Formula | Calculation | Result |
|---|---|---|
| Devine | 45.5 + (2.3 x 5.0) | 56.9 kg |
| Robinson | 49 + (1.7 x 5.0) | 57.4 kg |
| Miller | 53.1 + (1.36 x 5.0) | 59.8 kg |
| Hamwi | 45.5 + (2.2 x 5.0) | 56.4 kg |
| Average | (56.9 + 57.4 + 59.8 + 56.4) / 4 | 57.7 kg (127.1 lb) |
Compare that to the 165 cm row in the reference table above (57.7 kg) and it matches exactly, which is the point of that table: it’s just this same calculation run at every height.
Ideal weight versus the healthy BMI range
Ideal weight and a healthy weight range answer different questions, and mixing them up is where most confusion starts. Ideal weight is one point estimate from a formula. The healthy range is a band, calculated from BMI 18.5 to 24.9: minimum = 18.5 x height in meters squared, maximum = 24.9 x height in meters squared.
For the 175 cm man above, that range is 56.7 to 76.3 kg (125.0 to 168.2 lb). His formula average of 70.0 kg sits well inside it, closer to the middle than either edge. For the 165 cm woman, the range is 50.4 to 67.8 kg (111.1 to 149.5 lb), and her average of 57.7 kg again falls comfortably inside, not particularly close to either boundary.
That’s the useful takeaway from both examples: a weight doesn’t need to match the ideal-weight formula’s exact output to be healthy. The formula gives one plausible target; the range shows how much room exists around it. Someone weighing 65 kg at 175 cm is 5 kg under the Devine ideal weight and still solidly within the healthy band.
Calculate with your own numbers
Enter your height and sex below to see all four formulas, their average, and your healthy weight range at once.
Common mistakes and limitations
Treating one number as a strict target. All four formulas came from population data collected decades ago, not from a study of you specifically. An average of 70.0 kg for a 175 cm man is a reasonable reference point, not a number to chase to the decimal.
Confusing ideal weight with the healthy BMI range. These are two separate calculations answering two separate questions, as shown above. A weight several kilograms off the formula average can still land inside 18.5 to 24.9 BMI, which is the more medically grounded of the two.
Ignoring muscle mass and frame size. The formulas only take height and sex as input. A heavily muscled person can weigh 15 or 20 kg above every formula’s output and still carry low body fat, because none of these equations can tell muscle from fat. Someone with a naturally larger or smaller frame at the same height faces the same blind spot.
Overlooking why the sexes differ. It isn’t that the per-inch increase is dramatically different between men and women, Devine even uses the identical 2.3 slope for both. The gap comes from the starting weight at 5 feet, which every formula sets lower for women.
Dismissing Devine as outdated. It’s the oldest and simplest of the four, but it’s also the one still used to calculate drug dosing in clinical settings, particularly for medications where dosing by actual body weight would be inappropriate for a very heavy or very light patient. Simplicity is exactly why it stuck.
Frequently asked questions
Why do four different formulas give four different answers for the same height? Each one comes from separate research, done at different times with different populations, so the base weight at 5 feet and the amount added per inch don’t line up exactly. Devine, Robinson, Miller and Hamwi are all attempts at the same estimate, just calibrated slightly differently. Averaging them, as the worked examples above do, gives a more balanced figure than trusting any single one.
Is there a formula that works for children? No. All four were built from adult data and assume adult skeletal proportions, so none of them apply to a growing child or teenager. Pediatric weight assessment uses age- and sex-specific growth charts instead.
Does ideal weight change with age? None of the four formulas include age as an input, so the calculated number stays the same at 40 as it was at 25 for a given height and sex. In practice, body composition shifts with age even when weight doesn’t, which is one more reason to treat the output as a reference figure rather than a fixed lifelong target.
Why does Devine matter more than the others in medical settings? Because certain drug doses are calculated from ideal body weight rather than actual body weight, especially for patients who are significantly overweight or underweight, where dosing by total mass could be inaccurate or unsafe. Devine’s formula became the standard reference for that calculation, so it shows up in clinical dosing guides far more often than Robinson, Miller or Hamwi.