What an ideal body weight calculator really tells you
Ideal body weight, or IBW, is the output of a handful of old equations that estimate a weight from height and sex. They did not come from studies of what keeps people healthy. They were developed to help clinicians scale doses of certain drugs, and they have been borrowed ever since as a quick "what should I weigh" answer. This page is honest about that: it shows what the three best-known equations produce side by side, next to the weight range that corresponds to a healthy adult BMI, and it explains why none of them is a target.
If you want a broader check of weight status, the BMI calculator uses the CDC adult categories, and the body fat calculator looks at composition rather than height alone.
The three formulas and their coefficients
Each formula starts from a base weight at 5 feet (60 inches, 152.4 cm) and adds a fixed number of kilograms for every inch above that:
- Devine (1974). Men: 50 kg + 2.3 kg per inch over 5 ft. Women: 45.5 kg + 2.3 kg per inch over 5 ft.
- Robinson (1983). Men: 52 kg + 1.9 kg per inch over 5 ft. Women: 49 kg + 1.7 kg per inch over 5 ft.
- Miller (1983). Men: 56.2 kg + 1.41 kg per inch over 5 ft. Women: 53.1 kg + 1.36 kg per inch over 5 ft.
The coefficients were read from the summary table in a 2000 review of ideal body weight equations by Pai and Paloucek in the Annals of Pharmacotherapy, which lists Devine (1974), Robinson and colleagues (1983) and Miller and colleagues (1983). One older formula, Hamwi (1964), is common on other sites but is left out here because its figures were not read from a primary table for this page.
Worked examples
A man who is 5 ft 10 in (177.8 cm). That is 10 inches over 5 feet. Devine gives 50 + 2.3 × 10 = 73.0 kg. Robinson gives 71.0 kg and Miller gives 70.3 kg. The three answers span 70.3 to 73.0 kg, a spread of 2.7 kg between formulas for the same person.
A woman who is 5 ft 10 in. Devine gives 45.5 + 2.3 × 10 = 68.5 kg, Robinson 66.0 kg and Miller 66.7 kg, from 66.0 to 68.5 kg.
A man who is 6 ft 3 in (190.5 cm). With 15 inches over 5 feet, Devine reaches 84.5 kg, Robinson 80.5 kg and Miller 77.4 kg. The formulas pull further apart as height increases because their per-inch slopes differ.
A woman who is exactly 5 ft (152.4 cm). Here the amount added is zero, so each formula returns its base weight: Devine 45.5 kg, Robinson 49.0 kg, Miller 53.1 kg.
The BMI-based range for comparison
The calculator also shows the weights at your height that give a BMI from 18.5 up to but not including 25, the range the CDC calls healthy weight for adults. For a height of 177.8 cm that is 58.5 kg up to just under 79.0 kg. It is the same formula used by the BMI calculator, run backwards. It is a screening range for populations, not a recommended weight for any individual, and the upper end is strictly below 25, so a weight exactly at that BMI is already in the next category.
Why heights below 5 feet are not supported
The equations are built as a straight line that starts at 5 feet. Below that point, the line would give a base weight minus a number of kilograms for every missing inch, and nothing in the original papers shows the equations hold there. Rather than extrapolate and present a made-up number, this calculator asks for a height of at least 5 ft 0 in (152.4 cm). The same reasoning applies to children and teens, who are outside the scope of the tool; it is for adults only.
Limits you should know about
- Not a health target. The equations come from dosing work, not from research on healthy weights.
- No dosing use. Do not use the output to calculate a drug dose. Clinicians choose dosing weights for specific drugs with specific rules.
- Age, build and muscle are ignored. A muscular person, an older adult and someone with a small or large frame can all be healthy well away from the formula.
- The formulas disagree. The spread between them is a fair measure of how loose the idea of one ideal figure is.
- Sex is binary in the source. The equations offer male and female coefficients only, and the calculator reproduces that choice rather than adjusting it.
Using the result sensibly
If you are wondering whether your weight is a concern, the numbers on this page are a prompt for a conversation, not a verdict. Blood pressure, blood sugar, cholesterol, waist size, fitness, medical history and how you feel all matter. If you want a deeper look at body composition, the lean body mass calculator compares three formulas, and the wider fitness and health calculators collect related tools. To turn a weight into daily energy needs, the calorie and TDEE calculator gives a maintenance estimate.
A short history of ideal weight formulas
The idea of a formula for ideal weight goes back to the mid-twentieth century, and several of the equations were first published in the 1960s and 1970s. Devine's 1974 formula was written to help estimate drug doses in people of different sizes. The versions by Robinson and Miller followed in 1983 as attempts to fit the same idea more closely. None of them started from outcomes such as long-term health, which is why they are better described as historical reference equations than as health advice.
How the three formulas differ
All three add a fixed number of kilograms per inch above 5 feet, but the slopes and base weights differ. Devine adds the same amount per inch for men and women and starts from a lower base for women. Robinson uses a steeper slope for men than for women. Miller uses the smallest per-inch increments of the three, but a higher base weight, so it tends to give higher figures for short people and lower figures for tall people than the others. That crossing pattern is why the three lines agree most closely near average heights and spread apart at the extremes.
When a range is more useful than a number
Because no formula is authoritative, a range is a more honest way to look at the result. The span between the lowest and highest of the three formulas shows how much room there is for disagreement, and the BMI-based range shows how wide the screening definition of a healthy weight is for your height. If your actual weight falls inside, near or outside the ranges, that is not a diagnosis, it is a reason to look at the other measures that matter, such as waist size, fitness, blood tests and how you feel, ideally with a professional who knows your history.
Frequently asked questions
What is my ideal weight?
There is no single answer. The formulas on this page give different results for the same height, and none was designed to say what you should weigh. Treat them as reference points only.
Which ideal weight formula is most accurate?
None is a measure of health, so accuracy is not well defined. They are historical estimates and they disagree by several kilograms. If you are choosing one for reading, understanding what each was designed for matters more than picking a favourite.
Is the ideal weight the same as a healthy weight?
No. A BMI-based range is a screening range for adults, and the historical formulas were built for drug dosing. Neither guarantees good health.
Can I use these numbers for medication dosing?
No. Dosing weights are chosen by clinicians for specific drugs, with their own rules. Never use this page to calculate a dose.
Why does the calculator stop at 5 feet?
The equations were written for heights of 5 feet and above, and the calculator does not extend them below that.
Do the formulas account for age?
No. Age, frame size and muscle mass are not in the equations, which is one reason the results are only rough guides.
Sources and limits of this page
Devine BJ, Drug Intelligence and Clinical Pharmacy 1974; Robinson JD and colleagues and Miller DR and colleagues, American Journal of Hospital Pharmacy 1983, with the coefficients read from Pai MP and Paloucek FP, Annals of Pharmacotherapy 2000; BMI categories from the CDC page About Adult BMI. Originals other than that table were not re-opened for this page. This page is educational information, not medical advice.