Ideal Weight Calculator: Four Formulas, Not One Answer
Enter your height and this page runs the four ideal weight formulas that clinicians actually use, side by side, and shows you how far apart they land. You get a range rather than one number pretending to be the truth, plus the healthy BMI band for your height, which is wider than all four. Nothing is stored and nothing is sent anywhere.
Current weight is only used to show how far you sit from the healthy BMI range. Leave it blank if you would rather not.
Four formulas put your ideal weight somewhere between
—
depending on which of the four you ask
The four formulas, one row each
| Formula | Ideal weight |
|---|
Three of these four were written for pharmacists working out drug doses, not for anyone deciding what to weigh. The healthy BMI range is the only line in this table that comes from health outcomes.
How we got your number
Devine 1974, Robinson 1983, Miller 1983 and Hamwi 1964, computed exactly as published. The BMI band uses the WHO cut-offs of 18.5 and 24.9.
Note: all four formulas were only defined for heights of 5 ft and above. Below that they are being extended downwards, which their authors never tested. Read the BMI range instead.
Why formulas from the 1960s and 1970s give women lower numbers
Look at the bases. Devine starts a man at 50.0 kg and a woman at 45.5 kg for the same five feet of height. Robinson widens the gap in the slope as well: 1.9 kg per inch for men against 1.7 for women. Hamwi is the starkest, 2.7 against 2.2. Nothing in physiology produced those gaps. They were reverse engineered from the Metropolitan Life Insurance tables of desirable weight, which were assembled from policyholders who had been medically examined between the 1930s and the 1950s. That sample was mostly white, mostly urban, mostly people who could afford life insurance, and the female half of it was smaller and more weakly sampled than the male half.
Miller, in 1983, refitted the whole thing and came out with a much flatter female slope of 1.36 kg per inch against Hamwi's 2.2. At 185 cm those two differ by about three kilos for a woman and by more than eight for a man, and for women they cross over at around 175 cm, so a woman just below that height gets a higher number from Miller and a woman just above it gets a higher number from Hamwi. Equations that swap places like that are not measuring anything real. The female half of all four is the part built on the thinnest data, and it is the part that has been redrawn most often.
Why ideal weight is the wrong question
A weight is one number that lumps together bone, muscle, fat, water and whatever you last drank. Two people at the same height and the same weight can have completely different amounts of each, and the health risk sits with the composition, not the total. This is why the formulas above can only ever be a rough bracket.
Three measurements do more work than any target weight:
- Waist circumference. Measured at the midpoint between the lowest rib and the top of the hip bone. Risk starts rising above 94 cm for men and 80 cm for women, and is clearly raised above 102 cm and 88 cm. A waist under half your height is the simplest version of the same rule.
- Strength and how you move. If your squat, your carry or your stairs are getting easier, you are gaining or keeping muscle. That shows up as no change on the scale while the body underneath changes a great deal.
- Blood markers. Fasting glucose or HbA1c, blood pressure, and the triglyceride to HDL picture. These move on a diet change within weeks and they are what the weight was standing in for all along.
If every one of those looks good, a weight above your Devine number is not a problem to solve.
What the four formulas are actually used for
In hospitals, ideal body weight is still calculated daily, and almost never to advise a patient. It sets the dose of drugs that distribute poorly into fat tissue, so a 140 kg patient does not get an aminoglycoside dose calculated on all 140 kg. It sets tidal volume on a ventilator, where the standard of 6 to 8 ml per kilogram of predicted body weight uses a height based equation for exactly this reason. It sets the denominator for creatinine clearance estimates.
That is the job these equations do well. Telling a healthy adult what to weigh is a job nobody ever asked them to do, and they were never tested at it.
Every formula on this page was built for something other than telling a healthy adult what to weigh. Hamwi came first, in 1964, as a bedside shortcut for dietitians writing diabetic meal plans. They needed a quick protein and calorie target, and a rough body weight got them there in seconds without a chart. Devine followed in 1974, and it was not a health equation at all: B. J. Devine published it in a pharmacy journal to standardise gentamicin dosing, because dosing an antibiotic on actual body weight overdoses heavier patients. Robinson and Miller both arrived in 1983, in the same kind of journal for the same kind of reason, each fitting a straight line to different data and each getting a different line.
That history explains the spread you can see above. Four equations, four sets of assumptions, and answers that drift further apart the taller the person is, until at six foot two the highest and the lowest are nearly ten kilos apart. None of them is more correct than the others, because none was ever validated against anything you would care about: how long you live, how well you move, what your blood work says. They were fitted to averages of a narrow population, and an average is not a target.
What the four do share is their shape. Each one starts with a base weight for a person of exactly five feet and adds a fixed amount for every inch above that. Change the base or change the slope and you change the answer, which is precisely what Robinson and Miller did to Devine. Nothing deeper is going on inside them, and knowing that makes the disagreement much less mysterious.
So the honest output is a range. The four values bracket a narrow band, and the healthy BMI band for your height is wider still, normally by fifteen to twenty kilos, because it was drawn from the weights at which people actually stayed well. Most adults who land anywhere inside it are fine. If you want one figure to act on, your waist measurement and the direction of the scale over a month tell you more than all four formulas together, and they at least were measured on you.
More free calculators
See the full list on the calculators page: the daily calorie calculator, the BMR calculator, the BMI calculator, the calories burned calculator and the recipe nutrition calculator.
Frequently asked questions
What is my ideal weight?
There is no single ideal weight, which is why this page gives you four numbers instead of one. A woman of 170 cm gets answers between roughly 61 and 63 kg from the four formulas, while the healthy BMI range for that same height runs from 53 to 72 kg. Enter your height above and you get your own four numbers and that wider range. The range is the honest answer.
Which ideal weight formula is most accurate?
None of them, in the sense you mean. Devine, Robinson and Miller were all published in pharmacy journals as a way to calculate drug doses, and Hamwi was a bedside rule for writing diabetic meal plans. Not one of the four was validated against health outcomes. Robinson and Miller were at least fitted to population data and are the more defensible two, but if you want a number tied to real evidence, use the healthy BMI range instead.
Is ideal weight the same as healthy weight?
No. Ideal weight is a single number from a formula. Healthy weight is a range, and for a given height it spans about 15 to 20 kg. The BMI band of 18.5 to 24.9 is where the mortality and disease data are flattest, and it is much wider than the four formulas suggest. Your weight can sit outside every ideal weight figure on this page and still be comfortably inside the healthy range.
Does ideal weight depend on age?
Not in any of these four formulas. They use height and sex and nothing else. That is a real limitation, because body composition shifts with age, adults lose muscle from their forties onward, and several large studies find a slightly higher BMI is protective after 65. A 70 year old and a 25 year old of the same height get an identical number here, which tells you how much precision to expect from it.
Does frame size change ideal weight?
The old Metropolitan Life tables these formulas descend from did split people into small, medium and large frame, with about 10 per cent between the extremes. None of the four equations kept that. Frame is usually estimated from wrist circumference or elbow breadth, and the measurement is unreliable enough that most clinical guidance dropped it. If your skeleton really is broad, read the top of the BMI range rather than the middle.
Why do the four formulas disagree?
Because each one picks a different base weight for a person of exactly five feet and a different amount to add for every inch above that. Hamwi adds 2.7 kg per inch for men, Miller adds 1.41 kg. At about five foot six the two cross and agree to within half a kilo, but at six foot two they are nearly ten kilos apart. The taller you are, the wider the spread, because the disagreement lives in the slope.
What should I look at instead of ideal weight?
Three things that were measured on you rather than on a reference population from decades ago. Waist circumference, where risk starts climbing above 94 cm for men and 80 cm for women and is clearly raised above 102 cm and 88 cm. Whether you are getting stronger, because muscle gained can mask fat lost on the scale for weeks. And your blood work, meaning fasting glucose, blood pressure and the triglyceride to HDL picture. Any one of those tells you more than a target weight does.
How this calculator works
Sources
- World Health Organization — obesity and overweight, BMI classification. www.who.int
- NHS — managing your weight. www.nhs.uk
This calculator is for general information and is not medical advice. It is not suitable if you are under 18, pregnant or breastfeeding, or being treated for an eating disorder or a condition that affects weight. Speak to your GP or a registered dietitian before acting on the numbers.