Ideal Weight Calculator

What "ideal body weight" really means

Ideal body weight (IBW) is a clinical estimate of a reasonable weight for a given height and sex. It is worth being clear about its origins: these formulas were not invented as fitness goals. They were created so doctors and pharmacists could calculate medication doses, anaesthesia, and ventilator settings that scale with lean body mass rather than total weight. That is why this tool reports four different formulas side by side instead of one "answer" — each was derived from different population data, and the range they agree on is far more meaningful than any single number. The tool computes Robinson (1983), Miller (1983), Devine (1974), and Hamwi (1964), and also shows the separate BMI-based healthy weight range for context.

How the four formulas work

All four share the same shape: a base weight for a person 5 feet (60 inches) tall, plus a fixed amount of weight added for every inch above 60. They differ only in those two constants, and each has separate values for male and female. The formulas take height in inches, which the tool computes from your centimeters or feet/inches entry, and return kilograms:

The female versions use lower bases and slightly different slopes (for example Robinson female is 49 kg + 1.7 kg/in), reflecting average differences in body composition and bone density across populations. After computing the base, the tool applies a frame-size adjustment of −10% for a small frame, 0% for medium, and +10% for a large frame, because the same height carries different healthy weights depending on bone structure.

A worked example

Take a 170 cm male with a medium frame. First convert: 170 ÷ 2.54 = 66.93 inches, which is 6.93 inches over the 60-inch baseline. Each formula then gives:

The four estimates cluster between about 65.2 and 66.7 kg, averaging roughly 66 kg — a tight band of about 1.5 kg. The visual gauge plots this range so you can see at a glance how closely the formulas agree. A small frame would shift every value down 10%, a large frame up 10%.

Reading it alongside BMI

Below the table, the tool shows the healthy weight range derived from Body Mass Index, using the standard 18.5–24.9 band. It works backward from BMI = weight ÷ height², so for 170 cm the healthy range spans roughly 53.5 kg to 72.0 kg. Notice this BMI band is much wider than the IBW cluster — that is expected. IBW gives a single point estimate built for dosing; BMI gives a whole healthy range. A reasonable reading is that the IBW figures sit comfortably inside the BMI healthy range, which is the normal result for a typical build.

Important limitations

• None of these account for muscle. A trained athlete can weigh well above their "ideal" figure while carrying very little fat. The formulas assume an average body composition.
• They ignore age and ethnicity. Body composition shifts with age, and the population data behind each formula does not represent everyone equally.
• Frame size is an estimate. The wrist-wrap method — thumb and middle finger around the wrist: overlap means small, touch means medium, gap means large — is a rough rule of thumb, not a precise measurement.
• No single formula is "correct." Devine is the most cited clinically; Hamwi is common among dietitians; Robinson and Miller were later refinements. Treat the spread as the answer.

Using the result wisely

Read IBW as one input among several, not a target to chase. For most people the healthy BMI range, waist measurement, body-fat percentage, and how you feel and function matter more than hitting a formula's number. These calculations are estimates for educational purposes; for personalised guidance — especially around medication dosing, pregnancy, or a medical condition — consult a healthcare professional. Everything here is computed in your browser, so your height and other inputs are never sent anywhere.