How "Ideal Weight" Is Calculated

"Ideal body weight" is one of the most confidently named numbers in health, and one of the most widely misunderstood. The formula behind it is simple, its origin is specific, and knowing that origin changes how much weight you should give the result.

The Devine formula

Our Ideal Weight Calculator uses the Devine formula, published by B.J. Devine in 1974:

Men:   IBW(kg) = 50 + 2.3 × (height in inches − 60)
Women: IBW(kg) = 45.5 + 2.3 × (height in inches − 60)

The structure is a base weight for a 5-foot (60-inch) frame, plus 2.3 kg for every inch above that. Note what it uses: height and sex, and nothing else. Not age, not build, not body composition, not activity.

A worked example

For someone 170 cm tall — which is 66.929 inches, so 6.929 inches above 60:

Men:   50 + (2.3 × 6.929)   = 65.9 kg
Women: 45.5 + (2.3 × 6.929) = 61.4 kg

Enter your height in either unit and the calculator handles the conversion.

Where the formula came from

This is the part that matters most, and it is usually left out.

The Devine formula was not derived from research into what weight makes people healthiest. It was developed for calculating drug dosages — clinicians needed a standardised weight estimate from height for medications dosed by body size. It has been used clinically for decades and does that job well.

It was never validated as a health-outcome target. There is no study behind it establishing that people at their "Devine weight" live longer or are healthier than people slightly above or below it.

Other formulas give other answers

Devine is one of several. Robinson (1983), Miller (1983), and Hamwi (1964) are all documented alternatives, and they give slightly different numbers for the same person.

That divergence is informative in itself. If there were one true ideal weight for a given height, these formulas would converge on it. They don't, because each encodes slightly different assumptions, and none is measuring a biological constant.

We use Devine because it is the most widely used clinically, and we label the result moderate confidence — a clinical heuristic based on height and sex alone, not a validated health target.

How to actually read your result

Treat it as a rough reference point, not a goal:

• A number near your result does not certify that you are healthy.
• A number far from your result does not mean anything is wrong, particularly if you are muscular or have an unusually light or heavy frame.
• The result ignores body composition entirely — see why ideal weight ignores your build.

For most people, a range is more useful than a single figure. The Healthy Weight Range Calculator derives one from WHO BMI cutoffs, and BMI gives population-validated context that Devine simply does not have.

The bottom line

The Devine formula estimates a weight from your height and sex using a formula built for drug dosing in 1974. It is a useful reference point and a poor target. Calculate yours on the Ideal Weight Calculator, then read ideal weight vs healthy weight range for a more defensible way to think about it.