What 'ideal weight' means here
The ideal body weight (IBW) formulas used by this calculator were not designed as beauty standards. They were created in clinical settings to estimate the weight at which drug dosing, ventilator settings and nutritional needs behave predictably for a given height and sex. Because the equations are simple, easy to apply and roughly track population health data, they became a common reference for “healthy weight”. The calculator shows several formulas side by side because they disagree — and the spread between them is a more honest answer than any single number.
The formulas
Each formula gives a base weight for a height of 5 feet (152.4 cm) and adds a fixed amount per inch above that.
Devine (1974) Men: 50.0 kg + 2.3 kg/in Women: 45.5 kg + 2.3 kg/in
Robinson (1983) Men: 52.0 kg + 1.9 kg/in Women: 49.0 kg + 1.7 kg/in
Miller (1983) Men: 56.2 kg + 1.41 kg/in Women: 53.1 kg + 1.36 kg/in
Hamwi (1964) Men: 48.0 kg + 2.7 kg/in Women: 45.5 kg + 2.2 kg/inDevine is the most widely used in medicine — it is the basis for dosing many drugs by lean weight. Robinson and Miller were later refits of the same idea against actuarial life-insurance data, which is why they give flatter slopes: taller people are assigned proportionally less extra weight.
Worked example
A woman who is 5 ft 6 in (66 in, so 6 inches over 5 feet):
Devine: 45.5 + 2.3 × 6 = 59.3 kg (130.7 lb)
Robinson: 49.0 + 1.7 × 6 = 59.2 kg (130.5 lb)
Miller: 53.1 + 1.36 × 6 = 61.3 kg (135.1 lb)
Hamwi: 45.5 + 2.2 × 6 = 58.7 kg (129.4 lb)The formulas cluster between 59 and 61 kg here. For a man of 6 ft 3 in (15 inches over), they diverge more: Devine gives 84.5 kg, Miller 77.4 kg — a seven-kilogram gap, which is the formulas telling you they were calibrated on people of average height.
How this compares with the BMI healthy range
| Height | BMI 18.5–24.9 range | Devine (men / women) | Robinson (men / women) |
|---|---|---|---|
| 5 ft 2 in (157 cm) | 45.9–61.8 kg | 54.6 / 50.1 kg | 55.8 / 52.4 kg |
| 5 ft 6 in (168 cm) | 52.1–70.1 kg | 63.8 / 59.3 kg | 63.4 / 59.2 kg |
| 5 ft 10 in (178 cm) | 58.6–78.9 kg | 73.0 / 68.5 kg | 71.0 / 66.0 kg |
| 6 ft 2 in (188 cm) | 65.4–88.0 kg | 82.2 / 77.7 kg | 78.6 / 72.8 kg |
The IBW formulas land in the lower-middle of the BMI healthy band for most heights. If your weight is above the formula figure but inside the BMI range, that is not a problem; the BMI range is the better guide to health risk, and body composition matters more than either.
What the formulas cannot see
- Muscle mass. A strength athlete can be 15 kg above every formula at 10% body fat. The formulas assume an average build.
- Frame size. Wrist circumference relative to height is a rough proxy: a large frame can reasonably carry about 10% more than the formula, a small frame about 10% less.
- Age. Adults tend to gain lean and fat mass into their fifties; a weight slightly above the formula is normal and, in older adults, associated with better outcomes than being underweight.
- Ethnicity. The formulas were derived largely from European and North American data. Health-risk thresholds differ across populations, which is why some countries use lower BMI cutoffs.
Using the result sensibly
Treat the calculator as a reference range, not a target to hit. A useful approach is to look at the spread between formulas, compare it with the BMI healthy band for your height, and then check body fat percentage or waist circumference, which track health risk more directly. If all three point the same way — weight above the formulas, BMI above 25, waist above half your height — that is a meaningful signal. If they disagree, the body composition measures win.