Four formulas, one range
Ideal weight formulas are old. Most were written to help doctors dose medication, not to tell you what to weigh. They take your height and sex and give a number. Different formulas give different numbers, and none is the final word.
This calculator runs the Hamwi, Devine, Robinson and Miller formulas side by side and shows the spread, so you get a range instead of one false-precision figure.
Why they disagree
Each formula was built on different data and different assumptions. Hamwi dates from 1964. Devine came a few years later and became widely used in medicine. Robinson and Miller were adjustments from the early 1980s. They start from a baseline weight at five feet and add a set amount for each extra inch.
The sex split exists because, on average, men carry more muscle and bone mass at the same height. The formulas build that in with a different baseline and a different step per inch.
For tall or short people, the gap between formulas grows. That's a sign to treat the output as a rough zone.
Which one is most accurate?
None. They're population shortcuts. They ignore frame size, muscle, age and where you carry weight. Averaging the four, as the tool does, is a reasonable way to smooth out their quirks.
Ideal weight versus healthy BMI
They're related but not the same. A healthy BMI range of 18.5 to 24.9 covers a wide band of weights for each height. The formulas land somewhere inside it for most people. If a formula says 65 kg and your BMI-healthy band runs from 56 to 76 kg, there's a lot of room around that figure.
You can be healthy anywhere in that band. Fitness, blood tests and how you feel are better guides than a single target.
Don't use it as a hard goal
A formula can't know your build. A heavily muscled person may be well above the range and in excellent health. Someone with a very small frame may feel their best below it. If you want to lose or gain weight, set a modest first step, like five percent of your current weight, and see how you feel.
Not medical advice. Talk to a doctor if you're concerned about your weight. Your inputs stay in your browser.
Example with real numbers
Take a woman who is 165 cm tall, about 5 feet 5. The Devine formula gives around 57 kg. Robinson gives about 57.1. Miller gives about 56.9. Hamwi lands near 58.9. Those fit within two kilograms of each other, and that's the sort of range you should read as 'about 57 to 59'.
A man at 180 cm, about 5 feet 11, sees Devine at 75, Robinson near 72.9 and Miller near 74.1. Again a spread of a couple of kilograms, not a single answer.
If your weight sits within five kilograms of that range and you feel well, the number has little to say.
What the formulas ignore
They were built from small groups decades ago and assume an average frame. They don't know your bone structure, muscle, ethnicity or age. A lean athlete with dense muscle can sit well over the 'ideal' and be perfectly healthy.
Waist size, blood pressure, blood sugar and fitness tell you more about health than a target weight. If you can walk briskly for 30 minutes, sleep well and have normal bloodwork, a few kilograms either way doesn't matter much.
Treat the output as a conversation starter with your doctor, not a goal handed down.
Using the range sensibly
If you want to change your weight, aim for a slow shift of half to one kilogram a week at most. Fast changes are hard to keep.
Re-check every few months, since weight, height and goals shift. Children and teens should use growth charts instead, because they are still growing.