Ideal Weight Calculator: How It Works
Ideal body weight formulas were built for clinical purposes — mainly drug dosing and ventilator settings — not for personal weight goals. Understanding what they were designed to do explains both why they are useful and why they should not be treated as a target to hit.
The four common formulas
All work from height above 152.4 cm (5 feet), and all give a single number rather than a range.
| Formula | Men | Women |
|---|---|---|
| Devine (1974) | 50 + 2.3 kg per inch over 5 ft | 45.5 + 2.3 kg per inch over 5 ft |
| Robinson (1983) | 52 + 1.9 kg per inch | 49 + 1.7 kg per inch |
| Miller (1983) | 56.2 + 1.41 kg per inch | 53.1 + 1.36 kg per inch |
| Hamwi (1964) | 48 + 2.7 kg per inch | 45.5 + 2.2 kg per inch |
For a 175 cm man (about 5 ft 9 in, so 9 inches over):
| Devine | 70.7 kg |
|---|---|
| Robinson | 69.1 kg |
| Miller | 68.9 kg |
| Hamwi | 72.3 kg |
A spread of 3.4 kg between formulas, all claiming to give the ideal. That spread is itself the most useful output: it demonstrates there is no single correct answer, only a range.
Why a healthy range beats a single figure
The BMI-derived healthy range is a more defensible reference, because it is a band rather than a point.
| Height | Healthy range (BMI 18.5–24.9) |
|---|---|
| 155 cm | 44 – 60 kg |
| 165 cm | 50 – 68 kg |
| 175 cm | 57 – 76 kg |
| 185 cm | 63 – 85 kg |
Roughly 19 kg separates the ends of the range at 175 cm. Two people at opposite ends can both be entirely healthy, and which end suits an individual depends on frame size, muscle mass and history.
What the formulas cannot see
- Muscle mass. A trained athlete routinely exceeds every ideal weight figure while being healthier than someone who matches it exactly.
- Frame size. Skeletal width varies substantially between people of the same height, and none of these formulas account for it.
- Age. Body composition changes across a lifetime; the formulas do not.
- Ancestry. Healthy ranges differ across populations, and these formulas were derived from a narrow one.
Where they are genuinely used
In clinical practice these formulas are still standard for calculating drug doses — particularly anaesthetics and chemotherapy, where dosing on actual weight in a person carrying substantial excess weight would be dangerous — and for setting tidal volume in mechanical ventilation, where lung size tracks height rather than weight. In both cases a single reproducible number derived from height is exactly what is wanted. That is a very different purpose from setting a personal goal.
A better way to set a target
Rather than aiming at a formula's output, consider: a weight at which you feel well and function well; a waist measurement below half your height; a body fat percentage within a healthy range; blood pressure, glucose and lipids in normal ranges; and a weight you can maintain without unusual restriction. Those describe health more completely than any number derived from height alone.
This page is general information, not medical advice. Speak to a doctor or registered dietitian about a weight goal appropriate to you, particularly if you have a health condition or a history of disordered eating.