The definition
Ideal body weight (IBW) is an estimated target weight for a given height, originally developed for medical purposes such as calculating drug dosages. It's calculated using one of several published formulas, all of which produce a single number rather than a range.
The four formulas behind the number
This site's calculator averages four of the most widely referenced formulas:
| Formula | Introduced | Original purpose |
|---|---|---|
| Devine | 1974 | Drug dosing calculations |
| Robinson | 1983 | Refinement of the Devine formula |
| Miller | 1983 | Alternative refinement with different constants |
| Hamwi | 1964 | Quick clinical estimation, originally for diabetes management |
Each formula starts from a base weight at 5 feet and adds a fixed amount per inch above that. Averaging all four smooths out the differences between them, and our calculator then adjusts the result ±10% for your body frame size.
Ideal weight vs. BMI
These are two different tools measuring related but distinct things:
- Ideal weight (IBW) gives one specific number per height, adjusted for gender and frame.
- BMI gives a wide "healthy" range (18.5–24.9 kg/m²) for any given height, without accounting for frame, gender or muscle mass at all.
Neither accounts for body composition directly — a muscular person can have a BMI in the "overweight" range and an ideal weight figure well below their actual healthy weight, simply because muscle is denser than fat.
Ideal weight vs. healthy weight range
"Healthy weight range" is usually the broader, more forgiving concept — a band of weights, often based on BMI, within which health risk is statistically lowest for the general population. "Ideal weight" from these formulas is a single point estimate, useful for quick reference or as a starting target, but not a strict number to hit exactly.
In short: think of ideal weight as a reference point for conversation and goal-setting, not a rule. Your genetics, muscle mass, age and overall health matter more than matching a formula exactly.
Why frame size is factored in
Two people of identical height can have very different bone structures. Wrist circumference relative to height is used as a simple, non-invasive proxy for frame size — a narrower wrist suggests a smaller frame, and a wider wrist suggests a larger one. This adjustment shifts the single formula-average number up or down by about 10%, producing a more personalised estimate than height and gender alone.
Limitations worth knowing
- These formulas were developed on limited, largely Western adult populations decades ago.
- They don't directly measure body fat percentage or muscle mass.
- They aren't validated for children, pregnant women, or highly athletic individuals.
- They should be treated as an informational estimate, not a medical diagnosis.