Ideal Body Weight Calculator

About the Ideal Body Weight Calculator

"Ideal body weight" is a reference weight worked out from height and sex alone. Four linear formulas are in common use — Devine (1974), Robinson (1983), Miller (1983) and Hamwi (1964) — and they give answers that can differ by several kilograms for the same person. This calculator shows all four side by side, with the working, so you can see how much they agree.

Next to them it shows the weight range that matches a healthy BMI for your height: 18.5–24.9 on the WHO scale and 18.5–22.9 on the lower cut-offs suggested for Asian populations. The formulas were designed as clinical reference weights — for estimating medicine doses or ventilator settings — not as personal goals, and they are unreliable below 5 ft (152.4 cm).

The four formulas

Each adds a fixed amount for every inch of height above 5 ft (60 in; 1 in = 2.54 cm):

• Devine (1974): men 50 kg + 2.3 kg per inch; women 45.5 kg + 2.3 kg per inch. It appeared in an article on gentamicin dosing and was taken up for drug-dose calculations; the NIH ARDS Network ventilation protocol uses exactly these equations as "predicted body weight".
• Robinson (1983): men 51.65 kg + 1.85 kg per inch; women 48.67 kg + 1.65 kg per inch — regression lines through the median weights of the Metropolitan Life Insurance height–weight tables. They are often quoted rounded as 52 + 1.9 and 49 + 1.7, which gives about 0.8 kg more for a 175 cm man; this calculator uses the paper's own coefficients.
• Miller (1983): men 56.2 kg + 1.41 kg per inch; women 53.1 kg + 1.36 kg per inch. The flattest line: highest of the four for short people and among the lowest for tall people.
• Hamwi (1964): men 106 lb + 6 lb per inch; women 100 lb + 5 lb per inch, a rule of thumb from diabetes diet planning. It is worked in pounds here and converted exactly (1 lb = 0.45359237 kg).

Worked example, Devine for a man of 175 cm: 175 ÷ 2.54 = 68.9 in, which is 8.9 in above 5 ft; 50 + 2.3 × 8.9 = 70.5 kg.

A 2000 review of where the equations came from found they are similar because they were all derived from the same kind of height–weight tables, so "any one of these equations may be used to estimate IBW" (Pai & Paloucek).

The healthy BMI weight range

BMI is weight (kg) ÷ height (m)², so the weight for any BMI is BMI × height². For 1.75 m: 18.5 × 1.75² = 56.7 kg and 24.9 × 1.75² = 76.3 kg — the WHO healthy range (WHO Technical Report Series 894).

A WHO expert consultation found that in Asian populations the risk of type 2 diabetes and heart disease rises at lower BMIs and identified 23 as the first public-health action point, so the range with the lower cut-offs ends at 22.9. Unlike the formulas, the BMI range is a range: many different weights within it are healthy. The BMI calculator shows all the WHO, Asian and Indian categories.

Why these are reference weights, not goals

• They use only height and sex: not age, frame, muscle or where fat is stored. A muscular person can be well above every formula and healthy; a body fat estimate or waist-to-height ratio says more about body fat.
• They were built for clinical arithmetic — scaling doses of some medicines, setting ventilator volumes, estimating needs in nutrition support. Doses are worked out by clinicians with specific protocols: never use a number from this page to dose a medicine yourself.
• Below 5 ft (152.4 cm) the lines are extrapolated beyond the heights they were made from and quickly become implausible (at 4 ft 6 in, 137.2 cm, Devine gives a woman 31.7 kg, a BMI below 17), so results are marked "extrapolated" and none are shown more than 6 inches below 5 ft.
• They are for adults. Children and teenagers are assessed with growth charts, and pregnancy, amputations and some illnesses need a clinician's own reference weight.

Sources

• Devine BJ. Gentamicin therapy. Drug Intell Clin Pharm 8:650-5
• Robinson JD et al. Determination of ideal body weight for drug dosage calculations. Am J Hosp Pharm 40:1016-9
• Miller DR et al. Determining ideal body weight (and mass). Am J Hosp Pharm 40:1622
• Hamwi GJ. In: Diabetes Mellitus: Diagnosis and Treatment. American Diabetes Association, 1964
• Pai MP, Paloucek FP. The origin of the "ideal" body weight equations. Ann Pharmacother 34:1066-9
• NIH NHLBI ARDS Network, mechanical ventilation protocol summary — predicted body weight
• WHO, Obesity: preventing and managing the global epidemic, TRS 894 (2000); WHO Expert Consultation, Appropriate body-mass index for Asian populations, Lancet 363:157-63

Limitations

• Heights from 100 to 250 cm are accepted; formula results are marked extrapolated below 5 ft and not shown below 137.2 cm (4 ft 6 in).
• The formulas ignore age, frame size, muscle and body-fat distribution, and do not apply to children, teenagers or pregnancy.
• Results are shown to 0.1 kg (or lb); the formulas themselves are only approximations, so differences of a kilogram or two between them carry no meaning.

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