Why Four 'Ideal Weight' Formulas Give Four Different Numbers

Built for drug dosing, not fitness goals

"Ideal body weight" formulas weren't originally created to give people a personal weight target — they were developed so clinicians could estimate a reasonable body weight for calculating medication dosages, especially for drugs where dosing by actual (rather than ideal) body weight could be unsafe in people carrying extra body fat.

Four formulas, four different eras

Hamwi (1964), Devine (1974), Robinson (1983) and Miller (1983) were each derived independently, using different reference populations and different regression approaches, decades apart. None of them were designed to replace or correct the others — they simply coexist as competing estimates that happen to still get used today.

Why the gap between them is informative

All four share the same basic structure — a base weight at 5 feet tall, plus a fixed amount added per inch above that — but use different base weights and different per-inch increments. Comparing all four for the same height shows a real-world example of how differently "ideal" can be defined depending on which decades-old dataset a formula happened to be built from.

What none of them account for

None of these formulas use body composition, frame size, or muscle mass — purely height and sex. A muscular, athletic person will often weigh meaningfully more than every one of these formulas suggests while still carrying a healthy body fat percentage, which is exactly why none of them should be treated as a personal target to hit.

Compare all four at once

Our Ideal Body Weight Calculator runs the Devine, Hamwi, Robinson and Miller formulas side by side from the same height input.