What this ideal body weight calculator estimates
Ideal body weight, often shortened to IBW, is a height-based reference estimate calculated from sex-specific historical equations. It is commonly used when a protocol needs a quick, standardized body-size value, especially when actual measured weight is not the value a worksheet was designed to use. People may encounter IBW in medication dosing rules, ventilation settings, nutrition planning, and older chart references built around these equations. This calculator puts four well-known methods—Devine, Hamwi, Miller, and Robinson—side by side so you can see where they agree and where they differ at the same height.
An IBW result is not a command, diagnosis, or universal healthy-weight target. These equations do not measure body fat, muscle mass, athletic build, age, ethnicity, pregnancy, edema, amputation, or personal health goals. They are compact reference formulas. Their practical value is consistency: when a guideline names one of these methods, the calculation can be reproduced quickly and transparently. For general comparison, looking across several formulas is more informative than treating one estimate as exact.
This calculator compares IBW estimates after you enter standing height, select centimeters or inches, and choose the reference sex used by the historical equations. Height is converted to inches internally because the four formulas are written relative to 5 feet, or 60 inches. Each estimate is shown in kilograms and pounds, along with the average of the four methods to show the middle of their range.
How to enter height for ideal body weight estimates
For an ideal body weight calculation, begin with standing height because height is the only numerical input used by these equations. If you know height in centimeters, enter the measured value and leave the unit set to centimeters. If you know it in inches, change the selector to inches first. The result panel repeats the normalized height in both units so you can confirm that the conversion reflects what you intended to enter. That check matters because a unit mismatch can create a surprising IBW estimate.
The next selection is reference sex. The Devine, Hamwi, Miller, and Robinson equations use different constants for male and female reference populations, so the calculator needs that setting to choose the appropriate set of constants. When using a result for a particular clinical protocol, follow that protocol's stated guidance. For education or comparison, choose the equation set that matches the reference standard you want to review.
After submitting the form, first confirm the height shown in centimeters and inches. Then compare the four named IBW estimates before relying on the displayed average. A narrow cluster means these historical formulas give similar results at that height; a broader cluster is a reminder that IBW is a set of approximations rather than an observed measurement.
If an ideal body weight estimate seems unusual, verify the unit selection, the standing height entered, and the intended reference sex. Also remember that this page reports a formula-based reference value, not a prescribed personal goal weight. Those checks resolve most apparent calculation problems.
How the ideal body weight equations calculate results
Every ideal body weight equation on this page begins with a base weight at 5 feet and applies a fixed kilogram change for each inch above or below 60 inches. Once reference sex is selected, height is the only numerical driver. Taller heights yield larger estimates because the equations add more per-inch increments; heights below 5 feet yield smaller estimates because the same linear relationship is extended below the baseline.
For the male reference equations, the constants used here are Devine 50 + 2.3 per inch, Hamwi 48 + 2.7 per inch, Miller 56.2 + 1.41 per inch, and Robinson 52 + 1.9 per inch. For the female reference equations, the constants are Devine 45.5 + 2.3 per inch, Hamwi 45.5 + 2.2 per inch, Miller 53.1 + 1.36 per inch, and Robinson 49 + 1.7 per inch. Different base values and increments are why the four IBW outputs do not usually match exactly.
Ideal body weight formulas used by this calculator
These ideal body weight formulas are applied directly after height is converted to inches. The expressions below use h for height in inches.
For this IBW calculator, there is no weighted score or generic multi-input model behind the results. It converts the entered height to inches, subtracts the 60-inch baseline, and applies each formula's own base and per-inch constant. The average shown in the results is simply the arithmetic mean of the four calculated IBW values; it is not a separate clinical equation.
Comparing the named formulas is useful because their historical constants are not identical. If a policy, order set, or worksheet calls for Devine, Hamwi, Miller, or Robinson specifically, use that individual result rather than substituting the four-formula average.
A worked ideal body weight example you can check by hand
For an ideal body weight example, enter 170 cm and select the female reference equations. The calculator first converts the height to inches:
It then determines the difference from the 5-foot baseline:
Applying the female ideal body weight formulas gives approximately 61.44 kg for Devine, 60.75 kg for Hamwi, 62.52 kg for Miller, and 60.78 kg for Robinson. Their average is about 61.37 kg, or about 135.3 lb. Small displayed differences can occur because the page calculates from the full converted height and rounds results for presentation.
This IBW example illustrates why the calculator displays every method. The estimates are close, but they are not identical: Miller is the highest here and Hamwi is the lowest, with a spread of about 1.78 kg. That may be modest for general reference, yet it still matters when a protocol requires one named equation.
Ideal body weight formula comparison at a glance
This ideal body weight table lists each formula's 5-foot starting value and its fixed increment per inch from 60 inches. A larger base shifts an equation upward at every height, while a larger per-inch increment makes its IBW estimate rise more quickly as height increases.
| Formula |
Male base at 5 ft |
Male kg per extra inch |
Female base at 5 ft |
Female kg per extra inch |
| Devine |
50 kg |
2.3 kg |
45.5 kg |
2.3 kg |
| Hamwi |
48 kg |
2.7 kg |
45.5 kg |
2.2 kg |
| Miller |
56.2 kg |
1.41 kg |
53.1 kg |
1.36 kg |
| Robinson |
52 kg |
1.9 kg |
49 kg |
1.7 kg |
The IBW calculator has no additional adjustment hidden behind these constants. Two entries with the same height and reference sex will receive the same estimate from a given equation. That transparency is one reason these methods remain useful as quick reference tools, even though they do not replace more detailed body-composition assessment.
Practical interpretation and limits of ideal body weight
An ideal body weight calculation is most useful when a practical rule already calls for an IBW reference value. In that setting, this page can reduce unit-conversion and arithmetic errors while making the selected equation clear. It does not determine what a person should weigh or whether a particular real-world weight is healthy.
IBW formulas should not be treated as a verdict about health, fitness, attractiveness, or day-to-day target weight. Body composition, strength, age, fluid status, and medical history can materially affect an appropriate real-world assessment. Two people of the same height can have very different circumstances, while these equations only use height and the selected reference-sex constants.
Ideal body weight is also distinct from related terms. Actual body weight is the scale measurement. Adjusted body weight is a different estimate used in some dosing contexts. Lean body weight and body surface area describe other constructs. When a protocol names one of those measures, use its relevant method rather than an IBW equation.
IBW estimates below 5 feet require additional caution. The equations here continue below 60 inches because their implemented relationships are linear, but interpretation is less settled outside their usual adult reference context. Similarly, very tall or unusually proportioned people may have needs that a simple height-only estimate does not represent well.
For a medical use of ideal body weight, verify height, identify the equation required by the protocol, calculate the named result, and document the method used. For general education, compare all four estimates, view the average only as a midpoint across formulas, and keep their height-based limitations in mind.
- Verify standing height and the selected unit before calculating IBW.
- Use the named equation when a protocol explicitly requires one.
- Read the average as a midpoint across formulas, not as a mandate.
- Use extra caution with pediatrics, pregnancy, amputations, edema, and unusual body composition.
- Confirm decisions affecting care with a qualified professional.
When ready, enter height below to compare the four ideal body weight equations. The result panel emphasizes the separate formula values so that clinically relevant differences are not obscured by the average.
Frequently asked questions about ideal body weight
What does ideal body weight mean in this calculator?
This calculator provides height-based reference estimates from the Devine, Hamwi, Miller, and Robinson equations. They are historical formulas used in some protocols, not individualized definitions of a healthy weight.
Which ideal body weight formula should I use?
Use the named method when a clinician, institution, or worksheet specifies one. Otherwise, reviewing all four results shows the range produced by common IBW equations.
Does the calculator work below 5 feet tall?
Because these equations are linear, the calculator extrapolates them below 60 inches. Results at shorter heights need more cautious interpretation because these simplified adult reference equations are not suitable for every situation.
Supply a height and reference sex to see Devine, Hamwi, Miller, and Robinson ideal body weight estimates.
Sources: Formulas as originally published — Devine (1974), Robinson et al. (1983), Miller et al. (1983), and Hamwi (1964) — each defined as a base weight at 5 ft plus a fixed increment per inch above 60 in. Height is converted at 2.54 cm per inch and weight at 2.2046 lb per kg.