Ideal body weight: what the four formulas actually mean

The four formulas in the ideal body weight calculator were not designed to tell you a "healthy" weight. They are drug-dosing references from the 1960s–1980s, and they should not be treated as health targets.

A brief history of each formula

Devine (1974)

The most widely cited of the four, Devine established a base of 50 kg for men and 45.5 kg for women, adding 2.3 kg for each inch above 5 feet. It was created to estimate drug doses that scale with body size, not to diagnose anything. It has not been updated since.

Robinson (1983)

Robinson started from 52 kg and added 1.9 kg per inch, using the same base for both sexes. It was a refinement of the Devine approach, but still rooted in the same drug-dosing context.

Miller (1983)

Miller used 56.2 kg as the base and 1.41 kg per inch — a more generous base and a smaller per-inch increment, producing higher estimates at taller statures. Like Robinson, it was not intended as a health metric.

Hamwi (1964)

The oldest of the four, Hamwi used 48 kg (men) and 45.5 kg (women) with 2.7 kg per inch for men and 2.2 kg per inch for women. It is the formula most often seen in introductory nursing textbooks.

Why they diverge

Each formula reflects the population and assumptions of its era. Devine and Hamwi were derived from U.S. populations in the 1960s–1970s, when average body composition differed from today. The per-inch increments differ because each researcher assumed a different relationship between height and body mass.

At 5'9", the four formulas give values ranging from about 64 kg to 72 kg for men — a span of 8 kg. Neither the calculator nor the formulas claim one is correct. The spread itself is the point.

What they were not designed for

• Health risk assessment — BMI or waist circumference are better screens.
• Weight-loss goals — body-fat percentage is more useful.
• Children or teens — adult formulas do not account for growth.
• Clinical conditions — drug-dosing references are not nutritional guidance.

What to use instead

For a reference weight, the body fat calculator and BMI calculator together give a more complete picture: BMI screens broadly, and body-fat percentage tells you what share of your weight is fat versus lean.

Formulas are estimates, not medical advice.

Sources