“Ideal body weight” formulas were originally developed in a clinical context — to standardise medication dosing calculations, not to define a personal weight target. This calculator shows several of them side by side deliberately, because no single one is more “correct” than the others, and seeing the spread is more informative than seeing one authoritative-looking number.
Where these formulas actually came from
The Devine formula, still the most widely cited, was published in 1974 specifically to estimate a dosing weight for calculating drug dosages in clinical pharmacy — a practical shortcut for pharmacists, not a research finding about optimal human body weight. The Robinson, Miller and Hamwi formulas were derived similarly, each from different reference populations and each disagreeing with the others by several kilograms for the same height.
Why they disagree with each other
Each formula assumes a fixed relationship between height and a “normal” weight, calibrated against whatever population that formula’s authors had access to decades ago. None of them account for frame size, muscle mass, sex differences beyond a single offset, or the simple fact that healthy humans of the same height come in a wide range of builds. The spread between the four formulas shown here — often 3-5 kg for the same height — is itself the honest answer: there is no single correct number, only a rough range.
What a more useful frame looks like
Modern guidance tends to favour a healthy BMI range (typically 18.5-24.9) combined with waist circumference and overall body composition, rather than a single target weight from a height-only formula. Two people at the same height with very different muscle mass can both be perfectly healthy at quite different weights — something none of these formulas can see, since they only take height as input.
Use this as context, not a target
This tool exists to show that “ideal weight” is a much fuzzier concept than a single calculator output suggests. Weight is one data point; overall health depends on far more than that, and a healthcare provider looking at the whole picture is a better source of a personal target than any formula, this one included.