Ideal Weight Calculator

None of them is definitively most accurate, because true ideal weight depends on individual factors these formulas can't capture. All four were validated on limited populations decades ago and none accounts for your frame size, muscle mass, or age. In practice they cluster fairly close together: Robinson tends to give the lowest estimates and may suit smaller-framed people, while Miller and Hamwi run higher. The most sensible approach is to treat the average of all four as a rough starting point and the healthy BMI range as the wider target. Because body fat percentage reflects health better than scale weight, pair these numbers with a body-composition measure rather than chasing one exact figure.

Because each was built from a different study population and uses a different base weight and per-inch increment. Hamwi (1964) came from clinical observations, Devine (1974) extrapolated from limited dosing data, and Robinson and Miller (1983) applied corrections from newer research. Since every formula adds a fixed amount of weight for each inch above 5 feet — but a different amount — their estimates start close together near average heights and spread apart the further you are from that midpoint. So a person of average height may see all four within a few pounds, while someone very tall or very short can see a 10-pound or larger spread. That divergence is expected, which is why no single number is authoritative.

Largely, yes — these formulas can significantly underestimate a healthy weight for muscular people. Muscle is denser than fat, so the formulas, which assume average body composition, treat extra muscle the same as excess fat. If you strength-train regularly and carry above-average muscle mass, your healthy weight may sit well above a formula's number, and a higher scale figure can be perfectly healthy. What matters more is body composition: someone lean and muscular at a higher weight is generally healthier than someone at a lower weight with a high body fat percentage. Rather than aiming for a formula's "ideal," track body fat percentage and waist measurement, and discuss a realistic target with a healthcare provider or trainer.

Because the original formulas were built only around height and gender and never included an age adjustment. Each returns the same number for a 25-year-old and a 75-year-old of identical height, even though body composition shifts with age as muscle mass declines and fat distribution changes. Research since these formulas were published suggests that a slightly higher weight may be protective in older adults, while younger adults often do well toward the lower-middle of the healthy range. If you are older, the upper end of the formula results or the healthy BMI range may be more appropriate than the single average. Age is one more reason to treat these figures as approximate and confirm a target with your doctor.

The BMI range gives a band of healthy weights, while the formulas pinpoint a single number. The range shows every weight that produces a BMI between 18.5 and 25 for your height, so it spans a low and a high value; the Hamwi, Devine, Robinson, and Miller formulas instead each estimate one specific "ideal" figure. The range is often the more useful guide because it explicitly acknowledges that healthy bodies vary, and the formula results typically fall somewhere inside it. Treat the band as your healthy target and the formula average as a reference point within it. BMI itself has limits — it can't tell muscle from fat — so consider body composition too, and consult a healthcare provider for personalized advice.