Glossary
What Is Ideal Body Weight? Four Formulas Compared
Definition
Ideal body weight (IBW) is a figure computed from height and sex alone by a simple formula. The four classic formulas give different answers, and none is a target for any individual.
Last reviewed
"Ideal body weight" sounds like a verdict, but it began as a practical tool. The classic formulas were written so that clinicians had a quick reference weight for a given height, for example when working out medication doses. They take two inputs, height and sex, and return a single figure. They know nothing about your build, age, muscle or what you want to achieve.
That is worth holding on to, because the phrase suggests more than the maths delivers. The formula is a convention for comparing heights, not a measurement of the weight at which you are at your best.
The four formulas
Each formula starts from a base weight at 5 feet (60 inches) and adds a fixed amount for every inch above that. CalorTracker's ideal weight calculator shows all four, because they disagree and showing only one would hide that:
- Devine (1974)
- Robinson (1983)
- Miller (1983)
- Hamwi (1964)
Their exact constants, for men and for women, are in the table on how we calculate, and each paper is cited on sources. Women have different base weights and different amounts per inch than men in every formula.
Worked example
For a man 180 cm tall, which is 70.9 inches, the height over 5 feet is 10.9 inches. Applying each formula to that gives:
| Formula | Ideal weight |
|---|---|
| Robinson (1983) | 72.6 kg |
| Miller (1983) | 71.5 kg |
| Devine (1974) | 75 kg |
| Hamwi (1964) | 77.3 kg |
The four answers span 5.8 kg for the same man. That spread is the honest message of the table: even among the formulas themselves there is no single figure, so a result from any one of them should be read as a reference point and not a goal.
What it is and is not used for
The formulas are sometimes used as a rough comparison, for example to see roughly where a weight falls against a height. BMI does something similar with a range instead of a point. Neither says anything about body composition: a muscular person and a person with little muscle at the same height get the same answer. For composition, see body fat percentage.
Ideal body weight is also separate from your energy needs. Your daily calorie target comes from BMR, activity and the size of any calorie deficit, not from a formula for a reference weight.
What the formulas do not tell you
They were derived for adults, they cannot reflect age or build, and they were never intended to set a personal goal. The calculators on this site are not offered for children or for pregnancy. If you are thinking about your weight in relation to your health, a doctor or registered dietitian can look at the full picture, which a height-based formula cannot.
Where to use it
Sources
- Devine BJ. Gentamicin therapy. Drug Intell Clin Pharm 1974;8:650-655.
- Robinson JD, Lupkiewicz SM, Palenik L, Lopez LM, Ariet M. Determination of ideal body weight for drug dosage calculations. Am J Hosp Pharm 1983;40:1016-1019.
- Miller DR, Carlson JD, Lloyd BJ, Bauman SC. Determining ideal body weight (and mass). Am J Hosp Pharm 1983;40(10):1622-1625.
- Hamwi GJ. Therapy: changing dietary concepts. In: Danowski TS, ed. Diabetes Mellitus: Diagnosis and Treatment, vol 1. American Diabetes Association, 1964.
- How the figures above are computed: how we calculate. Every outside source we use is on sources.
This is general information, not medical advice. If you are pregnant, under 18 or managing a health condition, talk to a doctor or registered dietitian before changing how you eat.
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