Ideal Weight Calculator

What this ideal weight calculator estimates

The tool compares four height-based equations: Devine, Robinson, Miller and Hamwi. Alongside them it shows the weight range that corresponds to BMI 18.5–24.9. Treat all five as reference arithmetic. The headline figure is the midpoint of Devine and Robinson, and the four-formula spread underneath it gives the lowest and highest of the comparison results.

Drug dosing is where these equations came from. Robinson and colleagues’ 1983 paper describes deriving them for dosage calculations, and a later research paper on ideal weight and BMI traces how the four drifted apart from each other and from the old insurance height-weight tables.

The formulas used in this tool

Let X be the number of inches above 5 feet (152.4 cm). Devine, Robinson and Miller give kilograms. Hamwi below gives pounds, converted with 1 lb = 0.45359237 kg.

The Robinson coefficients here are the rounded version most calculators use. The original paper prints exact regression coefficients, so a tool built from those will hand you an answer a few hundred grams away from this one.

Illustrative weight estimates by height

The BMI column runs the same arithmetic for men and women. It has no input for your muscle mass, your limb proportions, or any medical condition you are managing.

Worked example: 175 cm

175 cm is 68.90 inches, or about 8.90 inches above five feet. For the male equations, Devine gives 70.5 kg and the rounded Robinson formula gives 68.9 kg. Their midpoint is 69.7 kg. Miller gives 68.7 kg and the pounds-based Hamwi equation gives 72.3 kg. That spread, 68.7–72.3 kg, is how far the four equations disagree over one identical height. The BMI-based range is about 56.7–76.3 kg.

Where the word “ideal” breaks down

Height and sex are the only two things these formulas know about you. They have no way to see your body composition or your medical history, and they cannot tell you whether losing or gaining weight would help you at all. Your doctor weighs up blood pressure, bloods, symptoms and history before saying anything about a weight target. Do not use this page to work out a medication dose.

Below 152.4 cm there are no inches above five feet left to count. The four height-based formulas come back marked unavailable and you get the BMI-based range by itself. The adult BMI interpretation applies from age 20.

Use the BMI calculator to see the category for your current height and weight. The body fat calculator estimates a different measure using a tape; the calorie calculator estimates daily energy needs.

Why Hamwi can differ between calculators

This tool implements Hamwi’s pounds-based equations, as reproduced in Peterson and colleagues’ comparison of ideal-weight equations, Table 3. Some calculators use rounded kilogram coefficients, which can give a slightly different answer. The formula table states the version used here.

A wider spread tells you how much the choice of equation moves the answer for identical inputs. Picking a favourite among the four is guesswork. None of them measures body composition, and none was built to set one person’s target weight.

Copy or print your calculation

Open How your result is calculated and you get the inch conversion, all four equations worked through with your height, and the two BMI bounds. The steps run the same equations as the headline figure, with intermediate numbers rounded so they read cleanly.

Copy results puts your inputs, the labelled results, the calculation steps and the notes on your clipboard. Print / save PDF opens a report preview and then your browser’s print dialogue, where Save as PDF is usually one of the options. Read the report before you send it to anyone, because it carries the measurements you typed in. Reset example puts the sample values back and leaves your unit choices alone. All of this happens in your browser, and the tool keeps no history of your calculations.

Common questions

Why do Devine and Robinson give different weights?

They start from different base weights and add different amounts per inch. For men, Devine adds 2.3 kg an inch and Robinson adds 1.9, so the gap between them widens the taller you are. Both were fitted to population averages, so neither one can single out a correct weight for you.

Is the midpoint my target weight?

No. It averages two formula estimates so you can see how far apart they sit. Use it to compare the equations, and take any decision about gaining or losing weight to your doctor.

Can I enter feet and inches?

Yes. Select feet and inches for height. Select kilograms or pounds separately for the results.

What happens below five feet?

You get the adult BMI-based range. The four height-based results come back blank, because stretching those equations below their reference height would invent numbers.

Does age affect these equations?

All four leave age out. A 22-year-old and a 70-year-old of the same height and sex get the identical answer, which is a good reason to read them as educational arithmetic for adults.

Written and maintained by Rowan Hale, the site author’s pen name. Updated September 13, 2026. No medical or dietetic qualification is claimed. Read our editorial policy or report a calculation error.