Ideal Weight Calculator

"Ideal body weight" is a decades-old concept from clinical medicine, originally developed to give doctors a fast, consistent way to estimate a patient's target weight — most notably for calculating medication doses — using nothing more than height and sex. Four formulas dominate this space today: Devine, Robinson, Miller, and Hamwi. None of them was designed to define a universally "correct" weight for any individual, and they routinely disagree with each other by several pounds at the exact same height. Understanding where they came from and what they were built for makes that disagreement much easier to interpret.

Before any of these four formulas existed, the earliest widely used height-weight reference was the Broca index, developed by French surgeon Paul Broca in the 1870s as a simple rule of thumb: ideal weight in kilograms roughly equals height in centimeters minus 100. It predates modern clinical dosing needs by nearly a century and has been superseded by the more carefully derived formulas below, but its basic logic — a simple linear relationship between height and a “target” weight — set the template every subsequent formula on this page still follows.

What "ideal body weight" actually means

Every formula on this page shares the same basic shape: a base weight assigned at a reference height of exactly 5 feet (152.4 cm), plus a fixed weight increment added for every inch of height above that baseline. The formulas differ only in their base weight and their per-inch increment — both of which were derived by different researchers, at different times, using different reference populations.

It’s important to be direct about what these formulas are — and aren’t. They were built to solve narrow clinical problems, chiefly standardizing medication dosing calculations so that two doctors treating patients of the same height would arrive at similar dosing decisions. They were never intended as a personal fitness or aesthetic target, and they say nothing about muscle mass, bone density, frame size, or individual health. Despite that, they’ve become widely used online as general “what should I weigh” reference points — a use case they can inform, but shouldn’t be treated as authoritative for.

The four formulas compared

(“kg/in” above means kilograms added per inch of height above the 5-foot baseline.)

Hamwi (1964) was the earliest of the four, developed by Dr. George Hamwi as a fast bedside reference for dietitians estimating patient targets without needing a lookup table. Devine (1974) became the formula most associated with medication dosing — it’s still the version most frequently cited in pharmacy references today, largely because it was adopted early into clinical dosing protocols and has stayed there through institutional inertia as much as demonstrated superiority. Robinson (1983) and Miller (1983) were both published the same year as independent refinements, using updated population data; Miller in particular tends to produce the highest estimate of the four because of its higher base weight and lower per-inch increment.

The roughly 10-pound spread in this example is typical, not an error in any one formula — it’s simply what happens when four different research groups, working decades apart with different data, each tried to answer a similar question with a similarly-shaped equation.

The same pattern holds for women, with a similar relative spread:

For this example the four formulas actually cluster slightly tighter for the woman than for the man above, with Miller running a bit higher than the other three — but this is specific to these two example heights rather than a general rule; the relative spread between formulas shifts depending on height, since each formula’s base weight and per-inch increment interact differently as height changes.

Why medication dosing needs a formula like this at all

The clinical motivation behind these formulas is worth understanding, since it explains a lot about why they’re built the way they are. Many medications — particularly those that don’t distribute well into fat tissue, including several classes of antibiotics, anesthetics, and chemotherapy agents — need to be dosed based on an estimate of a patient’s “normal” lean body size rather than their actual total weight. Dosing purely by actual weight can meaningfully over-medicate a patient carrying a higher proportion of body fat, since the drug doesn’t distribute evenly through fat tissue the way it does through lean tissue. Before these formulas existed, dosing decisions for such patients required either a body composition test (impractical for routine, fast-turnaround clinical decisions) or simply a clinician’s judgment call.

Devine’s formula in particular became the go-to reference for exactly this reason: it gave hospital pharmacists and physicians a standardized, reproducible starting point for dosing calculations without requiring a body composition scan for every patient. That’s also why it remains the most cited of the four today in pharmacy references, even though Robinson and Miller were both published as attempts to improve on it with updated data — clinical practice, once standardized around a specific formula, tends to be slow to switch even when a modest refinement becomes available.

Why the formulas disagree

Three factors explain most of the spread between formulas at any given height: the era and population each was derived from, the specific statistical method used to fit the base-weight-plus-increment shape to that data, and the clinical purpose each was optimized for. A formula built specifically for drug dosing (Devine) and one built as a general dietary reference (Hamwi) were solving related but distinct problems, and their authors made different judgment calls about how conservative or generous the resulting estimate should be.

None of the four accounts for frame size, muscle mass, bone density, or ethnicity — variables known to meaningfully affect what a genuinely healthy weight looks like for a specific individual. A 2016 review in the American Journal of Clinical Nutrition that attempted to reconcile these formulas into a single unified model found that no single equation consistently outperformed the others across diverse populations — reinforcing that the right way to use any of them is as a rough reference range, not a precise target.

The BMI-based healthy weight range

Alongside the four named formulas, this calculator also shows a healthy weight range derived directly from the standard BMI categories (18.5–24.9), which offers a genuinely different way of framing the same question — a range rather than a single number.

For most heights, this BMI-derived range is noticeably wider than the spread across the four named formulas — often 15–20 lbs from bottom to top rather than the roughly 10 lbs typical among Devine, Robinson, Miller, and Hamwi. That width is arguably more honest: it reflects the genuinely wide range of body weights consistent with good health at a given height, rather than converging on a single number that implies more precision than the underlying science actually supports.

Frame size: the variable none of these formulas measure

None of the four named formulas asks about frame size, yet skeletal frame is one of the more meaningful individual factors affecting what a healthy weight looks like at a given height. A common (though informal) adjustment applied on top of any of these formulas is ±10% for small or large frames respectively — someone with a naturally larger bone structure and wrist circumference might reasonably sit above the unadjusted formula result without that representing excess fat, while someone with a smaller frame might reasonably sit below it.

Frame size is typically estimated from wrist circumference relative to height, sometimes expressed as a simple ratio: height (cm) divided by wrist circumference (cm). Values above roughly 10.4 (men) or 11.0 (women) suggest a smaller frame; values below roughly 9.6 (men) or 10.1 (women) suggest a larger one, with everything in between considered medium. There’s no single universally standardized version of this test, though — different clinical references use slightly different cutoffs — which is part of why frame size isn’t built directly into any of the four core formulas as a variable. It’s better understood as a manual adjustment a clinician or individual can layer on top of the formula result than as something the formulas themselves account for.

How to use an ideal weight result responsibly

The most defensible way to use any of these formulas — or their average — is as a loose reference point for a conversation, not as a rigid personal target. A meaningful gap between your current weight and the formula average is worth discussing with a healthcare provider, who can weigh it against your actual body composition, health history, and goals. A small gap, on the other hand, especially for someone with an athletic build or larger-than-average frame, may not represent anything meaningful at all.

This is exactly why the calculator above shows all four formulas individually rather than only the average, and pairs them with the wider BMI-based range: the goal is to give a fuller, more honestly uncertain picture rather than a single falsely precise number.

What these formulas don't account for

Beyond frame size, several other factors that meaningfully affect a genuinely healthy weight for an individual sit entirely outside what any of these four formulas can see. Age is one: body composition shifts over a lifetime, with lean mass typically declining and fat mass typically rising even at a stable total weight, meaning the same formula result may represent a different health picture at 25 versus 65. Muscle mass is another — an athlete carrying substantially more muscle than average will have a higher healthy weight than these formulas suggest, without that representing excess fat in any sense. Ethnicity affects typical body composition and associated health risk at a given weight too, similar to the population differences already well documented for BMI cutoffs.

None of this means the formulas are useless — they remain a reasonable, fast starting point precisely because they’re simple and don’t require any equipment beyond a tape measure. It means they’re best treated as exactly that: a starting point for a broader conversation about individual health, not a standalone verdict. Pairing an ideal weight estimate with a body fat percentage reading, a waist-to-hip ratio, and an honest look at training history and family health background gives a far more complete picture than any single number — from this calculator or any other — ever could on its own.