Ideal Weight Calculator

Why Four Different Formulas?

Ideal weight formulas were developed at different times, for different original purposes (several were created for medication dosing estimates), and none of them is definitively "correct." Showing all four together gives a more honest picture, a range rather than a single falsely precise number, since real healthy weight depends on much more than height and sex alone.

Why Sex Is a Required Input

Every one of these four formulas uses a different base weight and per-inch multiplier depending on sex, generally reflecting average differences in typical body composition and frame size between men and women at a population level. This is the same underlying reasoning found in other body composition formulas, like BMR and body fat calculators, that also branch by sex. It's worth remembering these are population averages baked into decades-old formulas, not a claim that any specific individual must fit the pattern their sex category implies.

Healthy BMI Range

As an additional reference, this calculator shows the weight range that would put you within the standard "normal" BMI category (18.5–24.9) at your height. Like the other formulas, BMI has well-known limitations, it doesn't distinguish muscle from fat, so this is one data point among several, not a definitive target.

Worked Example

For a man 170 cm tall, the calculator first converts height to inches (66.9 in) and finds the amount over 5 feet, 6.9 inches. Each formula applies its own base weight and per-inch multiplier to that figure: the Devine formula gives 50 + 2.3 × 6.9 = 65.9 kg, the Robinson formula gives 52 + 1.9 × 6.9 = 65.2 kg, the Miller formula gives 56.2 + 1.41 × 6.9 = 66.0 kg, and the Hamwi formula gives 48.0 + 2.7 × 6.9 = 66.7 kg. Averaging all four gives 65.9 kg. Separately, the healthy BMI range for that same 170 cm height works out to 53.5–72.0 kg (18.5 and 24.9 multiplied by height in meters squared), a considerably wider band than the roughly 1.5 kg spread across the four named formulas. For a woman 160 cm tall, the same process gives 52.4 kg (Devine), 54.1 kg (Robinson), 57.2 kg (Miller), and 52.1 kg (Hamwi), averaging to 53.9 kg, with a healthy BMI range of 47.4–63.7 kg at that height.

Why "Ideal Weight" Formulas Exist and Their Real Origin

Despite the name, none of these formulas were originally created to define an aesthetic or fitness ideal. The Devine formula, the most widely cited of the four, was published in 1974 specifically to help clinicians estimate a patient's lean body weight for calculating medication dosages, since dosing certain drugs based on total body weight (which includes fat) can be less accurate than dosing based on an estimate closer to lean mass. The Robinson (1983), Miller (1983), and Hamwi (1964) formulas were developed around similar clinical contexts. None were built from large, modern, diverse population studies the way contemporary BMI research has been, which is an important piece of context for why these numbers should be treated as rough historical reference points rather than authoritative modern health targets.

Common Mistakes When Reading These Results

The biggest mistake is treating the average of the four formulas as a precise, personally validated target weight rather than a rough historical reference point derived from decades-old clinical formulas built for an entirely different purpose. Another common mistake is ignoring the healthy BMI range entirely and fixating only on the narrower cluster from the four named formulas, when in practice the wider BMI band is often the more medically grounded reference of the two, since BMI research is based on much larger and more recent population studies. A third mistake is applying these results uniformly regardless of body type, someone with a naturally larger or smaller frame, more or less muscle mass, or an athletic background should weight these numbers even more loosely than someone with an average build, since none of the formulas can detect those individual differences from height and sex alone.

Limitations Shared by All Four Formulas

Because every one of these formulas relies solely on height and sex, none can distinguish between a lean, muscular frame and a less muscular one of the same height, and none accounts for age, ethnicity, bone density, or overall frame size, all factors that legitimately influence what a healthy weight looks like for a given individual. This is why a bodybuilder, a distance runner, and someone with a naturally larger bone structure can all show as meaningfully "above ideal" despite being in excellent health, and why these formulas function better as rough historical benchmarks than as personalized health targets. Modern approaches to assessing healthy weight typically combine multiple data points, BMI, waist circumference, body fat percentage, and overall health markers, rather than relying on a single height-based formula the way these tools do individually.

Ideal Weight vs Body Fat Percentage vs BMI

This calculator sits alongside two related but distinct tools on body composition. BMI, covered by the BMI Calculator, uses only height and weight and doesn't require choosing between multiple named formulas, giving a simpler but cruder single-category output. Body fat percentage, covered by the Body Fat Calculator, uses tape measurements to estimate actual fat mass rather than inferring a target weight from height alone, generally a more individualized measure since it responds to actual body composition changes rather than just the number on a scale. Ideal weight formulas like the ones here sit somewhere between the two, more specific than BMI's broad categories, but still based only on height and sex rather than any direct measurement of the individual. Using more than one of these tools together generally gives a fuller picture than relying on any single one.

How to Interpret a Range Instead of a Single Number

Rather than fixating on any single result, it's more useful to look at the overall spread these five figures (four formulas plus the BMI range) produce together. A tight cluster among the four named formulas, as in the worked example above where all four landed within about 1.5 kg of each other, suggests reasonable agreement across the different clinical models. The much wider healthy BMI range serves as an outer boundary, a weight within that band is generally considered within a medically reasonable range even if it falls outside the narrower cluster the four named formulas suggest. Reading the results this way, as converging evidence rather than a single verdict, better reflects what these tools were actually designed to provide.

Frequently Asked Questions