What is ideal body weight?
Ideal body weight (IBW) is a reference weight for a given height and sex, calculated with a simple formula. Clinicians use it mainly to dose certain medicines and set ventilator settings. Outside medicine it's a rough benchmark for comparing your current weight, not a measure of health or body fat.
This calculator uses the Devine formula, takes your height in centimeters, and shows one result in kilograms, rounded to one decimal place.
The Devine formula
The formula was published by B. J. Devine in 1974, in a paper on gentamicin dosing in Drug Intelligence and Clinical Pharmacy. It starts from a base weight at 5 feet (60 inches) and adds a fixed amount for each inch above that:
- Men: IBW (kg) = 50 + 2.3 × (height in inches − 60)
- Women: IBW (kg) = 45.5 + 2.3 × (height in inches − 60)
Devine didn't derive these numbers from a population study. They became the default largely because pharmacists and doctors adopted them for dosing, and they've been used that way ever since.
Worked example
A man who is 178 cm tall:
- Convert to inches: 178 ÷ 2.54 = 70.08 inches
- Inches above 5 feet: 70.08 − 60 = 10.08
- Multiply by 2.3: 10.08 × 2.3 = 23.18
- Add the male base: 50 + 23.18 = 73.2 kg
For a woman who is 165 cm (64.96 inches): 45.5 + 2.3 × 4.96 = 56.9 kg.
How Devine compares with other formulas
Several other ideal-weight formulas use the same structure, a base at 5 feet plus a fixed amount per inch. Each gives a slightly different answer:
| Formula | Men | Women | Man at 178 cm |
|---|---|---|---|
| Devine (1974) | 50 + 2.3 kg/in | 45.5 + 2.3 kg/in | 73.2 kg |
| Robinson (1983) | 52 + 1.9 kg/in | 49 + 1.7 kg/in | 71.1 kg |
| Miller (1983) | 56.2 + 1.41 kg/in | 53.1 + 1.36 kg/in | 70.4 kg |
| Hamwi (1964) | 48 + 2.7 kg/in | 45.5 + 2.2 kg/in | 75.2 kg |
This calculator reports Devine only. If your result sits between the Miller and Hamwi numbers for your height, you're within the spread these formulas produce. The spread is a useful reminder of how approximate any single number is.
How to use the result
- Enter your sex and height in centimeters. If you know your height in feet and inches, the length converter will convert it.
- Read the result as a reference point, not a goal.
- Compare it with the healthy BMI range for your height using the BMI calculator. For a 178 cm adult, a BMI of 18.5 to 24.9 corresponds to roughly 58.6 to 78.9 kg, a much wider band than any one formula gives.
Limits
- No frame size or muscle. A muscular person or someone with a large frame can be healthy well above their IBW.
- Short heights. Below 5 feet, the formula subtracts weight per inch and quickly gives unrealistic numbers. The calculator doesn't stop you entering heights down to 100 cm, so read results for short heights with caution.
- Adults only. It doesn't apply to children or teenagers, who are assessed with growth charts.
- Age isn't considered. The same number applies at 20 and at 80.
Related calculators
- BMI calculator: the healthy weight range for your height.
- Body fat calculator: estimates how much of your weight is fat.
- Calorie calculator: daily calories if you want to move toward a different weight.
- BMR calculator: your resting calorie burn.
This calculator is for general information and doesn't replace advice from a healthcare professional.
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