Ideal Body Weight Calculator

"Ideal body weight" (IBW) formulas were not originally created to define an aesthetic ideal — they were developed as quick clinical tools, mostly for calculating drug dosages. Many medications need to be dosed relative to a patient's body size, but using someone's actual weight can be misleading if that weight includes a large amount of excess fat (fat tissue does not process most drugs the way lean tissue does), so clinicians needed a fast, standardised way to estimate a patient's "normal" weight for a given height without a body composition scan. That practical, dosing-focused origin is why these formulas remain simple linear equations — a baseline weight at 5 feet, plus a fixed increment for every inch above it — rather than anything derived from population body-fat data. This calculator shows four of the most established IBW formulas side by side, since each was developed independently and none is considered definitively "correct" — clinicians and researchers still debate which performs best, and in practice they are usually used together as a plausible range rather than any single one being treated as the answer. The Devine formula (1974), the most widely cited and still the default in many drug-dosing calculators today, set men's baseline at 50.0 kg and women's at 45.5 kg for 5 feet, adding 2.3 kg per inch above that. The Robinson formula (1983) revised those coefficients using a larger reference dataset, giving 52 kg for men and 49 kg for women, with a smaller 1.9 kg and 1.7 kg per-inch increment respectively. The Miller formula (also 1983) used a different dataset again, arriving at higher baselines (56.2 kg men, 53.1 kg women) with smaller per-inch increments. The Hamwi formula, the oldest of the four (1964), was designed originally for quick diabetic diet planning in a clinical setting, with a men's baseline of 48.0 kg and women's of 45.5 kg, and the steepest per-inch increment of the group (2.7 kg for men, 2.2 kg for women). Because the four formulas use different reference populations and coefficients, they rarely agree exactly — for a given height, they typically span a range of several kilograms, which is exactly why this tool shows all four plus their average rather than picking one as definitive. A wider spread between the four results for a particular height is not a sign of an error; it reflects genuine disagreement in the clinical literature about the best simple linear approximation, which is precisely why body mass index (BMI) and its healthy-range band, rather than any single IBW figure, is the primary tool most modern clinicians actually rely on for weight assessment (see the BMI Calculator). All four IBW formulas share the same core limitation: they are pure functions of height and sex, with no allowance for body frame size, muscle mass, or body composition. A person with a naturally large skeletal frame or high muscle mass will have a real, healthy weight meaningfully above any of these formulas' output, and a naturally small-framed person will sit meaningfully below it — some clinicians apply a rough ±10% adjustment for frame size, but none of the four formulas here do so automatically. The formulas are also known to become less reliable at the extremes of height (well under 5 feet or well over 6'6"), since the reference populations they were built from rarely included people at those extremes. Treat the range this tool produces as a rough clinical reference point worth discussing with a doctor if you're curious, not as a personal target to hit — a healthy weight range depends on far more about an individual than height and sex alone can capture.