Ideal Weight Calculator

How ideal weight formulas work

"Ideal weight" has never had one universal definition, so over the decades several physicians proposed their own height-based formulas, mostly developed to estimate drug dosages accurately rather than as fitness targets. This calculator shows four of the most cited: Devine (1974), Robinson (1983), Miller (1983), and Hamwi (1964), then averages them into a single suggested figure.

All four formulas share the same structure: a base weight for 5 feet of height, plus an additional amount for every inch above that. The Devine formula, for example, uses 50 kg + 2.3 kg per inch over 5 feet for men, and 45.5 kg + 2.3 kg per inch for women. Robinson and Miller adjust those constants slightly based on different population studies, while Hamwi, developed for quick bedside use, tends to produce marginally lower figures. None of them factor in frame size, muscle mass, or age, which is precisely why looking at the range across formulas is more informative than fixating on any single number.

These formulas were built decades ago, largely from data on adults of average build, so they work best as a general reference rather than a strict target — especially for athletes, older adults, or anyone with an unusually large or small frame. A more complete picture combines this range with your BMI and body fat percentage, and ideally a conversation with a healthcare provider who can account for your muscle mass, bone density, and health history. Treat the number here as a reasonable midpoint to discuss, not a number to chase at all costs.

Frequently asked questions

Why do the different formulas give different numbers? Devine, Robinson, Miller, and Hamwi were each derived from different population samples and study eras, so they don't agree exactly — showing a range instead of one number is more honest about the uncertainty involved.

Is "ideal weight" the same as the healthiest weight for me? Not always. These formulas were originally built for drug-dosing calculations, not wellness targets, so they ignore muscle mass, frame size, and body composition. Use the range as a reference point, not a strict goal.

Does frame size change the result? In real life, yes — someone with a larger bone structure will naturally sit higher in a healthy range. These particular formulas don't adjust for frame size directly, which is one of their known limitations.

Worked example

For a woman 160 cm tall, the Devine formula gives ideal weight ≈ 45.5 kg + 2.3 kg per inch over 5 feet. At 160 cm (≈63 inches, 3 inches over 5 feet), that’s 45.5 + (3 × 2.3) = 52.4 kg.

Why do different formulas give different “ideal” weights? The Devine, Robinson, and Hamwi formulas were each built from different reference populations and rounding conventions, so results can vary by a few kilograms — treat the range across formulas as more meaningful than any single number.

Should athletes use this number? Not directly. These formulas were designed for medication dosing and general population screening, not for muscular builds — a bodybuilder or powerlifter will often sit well above the “ideal” figure while still being lean and healthy.