Ideal Weight Calculator

Where “ideal weight” formulas come from

There is no single ideal weight for a height. Healthy people of the same height differ in frame, muscle and where they carry fat, and a wide range of weights is compatible with good health. The formulas on this page are useful reference points, but they were created for narrower purposes than the name suggests.

• Hamwi (1964) is a rule of thumb from a chapter on diabetes treatment, written in pounds: 100 lb at 5 ft plus 5 lb per inch for women, 106 lb plus 6 lb per inch for men.
• Devine (1974) appeared in a paper on dosing the antibiotic gentamicin. Some drugs are better dosed on an estimate of body size without excess fat than on total weight, and Devine’s formula became the standard estimate for that purpose.
• Robinson (1983) and Miller (1983) are regression fits to the Metropolitan Life Insurance height-weight tables, made to check and refine Devine’s formula for drug dosing.

The insurance tables behind them listed weights linked to the lowest death rates among insured people — hence the words “desirable” and later “ideal”. A 2000 review by Pai and Paloucek traced these origins and concluded that the equations agree closely because the tables they come from agree, so any of them gives a similar estimate.

The calculator asks for sex because each formula has separate versions for men and women, built from tables that recorded only those two groups.

The formulas

Each formula starts from a base weight at 5 ft (60 inches) and adds a fixed amount for every inch above that:

The Robinson coefficients are the ones published in the paper; many websites round them to 52 + 1.9 and 49 + 1.7, which adds up to about 1 kg at average heights. Hamwi is computed in pounds and converted exactly (1 lb = 0.45359237 kg); rounded metric versions such as 48 kg + 2.7 kg per inch are also in circulation.

The healthy BMI range comes from the WHO adult classes, turned around to give weight:

Heights under 5 ft. The formulas were written only as “5 ft plus so much per inch”. Some people run them backwards, subtracting the per-inch amount, but none of the authors published that, and it soon gives odd results: Devine for a woman of 4 ft 8 in would be 36.3 kg (80 lb), a BMI of 17.9, below the healthy range. Below 5 ft, this calculator therefore shows only the healthy BMI range.

Worked example

A woman who is 5 ft 5 in (65 inches) tall, 5 inches over 5 ft:

1. Robinson: 48.67 + 1.65 × 5 = 56.92 kg (125.5 lb)
2. Miller: 53.1 + 1.36 × 5 = 59.9 kg (132.1 lb)
3. Devine: 45.5 + 2.3 × 5 = 57.0 kg (125.7 lb)
4. Hamwi: 100 + 5 × 5 = 125.0 lb (56.7 kg)
5. Healthy BMI range: height 1.651 m, squared 2.7258; 18.5 × 2.7258 = 50.4 kg (111.2 lb) to 24.9 × 2.7258 = 67.9 kg (149.6 lb)

The four formulas span 125.0 – 132.1 lb, equivalent to a BMI of about 20.8 to 22.0 — well inside the healthy range, which runs from 111.2 to 149.6 lb at this height. Being heavier than the formulas but inside the BMI range is not, on its own, a health concern.

What these numbers can’t tell you

• Body composition. Two people with the same height and weight can carry very different amounts of muscle and fat. The body fat calculator gives a rough measure of that.
• Frame size. The insurance tables had separate columns for small, medium and large frames, and Robinson’s paper also published frame-specific equations. The single-line formulas here are for all frames combined.
• Who they don’t cover. Children and teenagers, pregnancy, and people with medical conditions that affect weight. Health risks also begin at a lower BMI in some populations, so the healthy range may sit lower for people of Asian background.
• Dated data. The tables describe insured American adults measured decades ago, not today’s more varied population.