Plug the same height and weight into different "ideal weight" calculators and you'll often get noticeably different numbers — not because one is wrong, but because they're using genuinely different formulas.
The major formulas, briefly
The Devine formula (originally created in 1974 for drug-dosage calculations, not general health advice) is one of the most widely used. Robinson and Miller are later adjustments to Devine's original numbers. The Hamwi formula, developed around the same era, uses a similar height-based approach with its own slightly different constants. All of them are decades-old, height-based estimates — none were derived from large-scale modern body-composition data.
Why they disagree with each other
Each formula uses different base constants and increments per unit of height above a baseline, so even for the exact same height, the "ideal" weight each one outputs can differ by several kilograms — there's no single mathematically "correct" answer among them, just different historical approximations.
What none of these formulas account for
Muscle mass, bone density, frame size and body composition aren't factored into any of these height-only formulas — which is why an athletic, muscular person can show as "overweight" by these formulas despite having low body fat, a well-known limitation of height-weight-only approaches in general.
How to use the number sensibly
An ideal weight calculator is useful as a rough reference point or a starting conversation with a healthcare provider — not as a precise personal target, given how much the formulas disagree with each other and how little they account for individual body composition.
The bottom line
"Ideal weight" from any single formula is an old, height-only approximation — treat the range across multiple formulas as more informative than any single number.
Try it yourself
Put this into practice with our ideal weight calculator.