Ever typed your height into an “ideal weight” calculator and felt judged by the answer? That number was never meant to be a goal weight. It was built for doctors working out drug doses, so here is how to read it properly.
Where ideal body weight actually comes from
Ideal body weight (IBW) was introduced by Ben J. Devine in 1974 to estimate how fast the body clears drugs in obese patients. Researchers later found that the metabolism of certain drugs relates more closely to IBW than to total body weight. The idea was based on insurance data showing how mortality varied across different height and weight combinations.
That origin matters: it is a clinical shortcut, not a verdict on how you should look.
The two formulas you will meet most often
Both formulas use your height in centimetres and start from the same reference point, 152 cm. Every centimetre above that adds a fixed amount of weight.
Devine formula:
- Men: 50 kg + 0.9 kg × (height in cm − 152)
- Women: 45.5 kg + 0.9 kg × (height in cm − 152)
Hamwi method:
- Men: 48 kg + 1.1 kg × (height in cm − 152)
- Women: 45.4 kg + 0.9 kg × (height in cm − 152)
In plain language: start with a base weight for someone 152 cm tall, then add roughly one kilo for every extra centimetre.
A worked example at 170 cm
The height gap is 170 − 152 = 18 cm. Then:
- Devine, man: 50 + 0.9 × 18 = 66.2 kg
- Devine, woman: 45.5 + 0.9 × 18 = 61.7 kg
- Hamwi, man: 48 + 1.1 × 18 = 67.8 kg
- Hamwi, woman: 45.4 + 0.9 × 18 = 61.6 kg
The two methods land within about 1.6 kg of each other, which is why the formulas are said to give similar results. Compare that with the standard healthy BMI range of 18.5 to 24.9. At 1.70 m (1.70 × 1.70 = 2.89), that works out to 53.5 kg to 72.0 kg. Every IBW result above sits comfortably inside that range, but the range itself is about 18 kg wide.
More heights, same method
- 160 cm: Devine gives 57.2 kg (men) and 52.7 kg (women). The BMI range is 47.4 to 63.7 kg.
- 180 cm: Devine gives 75.2 kg (men) and 70.7 kg (women). Hamwi gives 78.8 kg (men) and 70.6 kg (women).
What the number cannot tell you
An IBW figure ignores what your body is made of. As the source puts it, IBW “is not the perfect fat measurement, as it does not show the fat or muscle percentage in one’s body.” A muscular athlete can be labelled overweight by a formula while being very fit and healthy. A scan such as dual-energy X-ray absorptiometry (DEXA) is what accurately measures fat, muscle and bone.
Body weight also moves during the day as the amount of water in your body changes, so a one-kilo difference between two weigh-ins means very little.
How to use it sensibly
- Treat the Devine or Hamwi result as one reference point, not a target.
- Check it against the BMI range for your height, then look at body composition if you train regularly.
- Remember where it is really used: clinicians use the Devine formula mostly to estimate kidney function for drug dosing, and some sports use weight classes instead.
Want to check your own range? Try the BMI calculator, and read how to read your BMI number to see why a single figure never tells the whole story.
