Ideal Weight Calculator
Four formulas are in common use and they disagree by several kilograms. That spread is the honest answer — all of them work from height alone, so none knows anything about your build.
Around
74.1kg
- Robinson
- 72.6 kg / 160.2 lb
- Miller
- 71.5 kg / 157.7 lb
- Devine
- 75.0 kg / 165.3 lb
- Hamwi
- 77.3 kg / 170.5 lb
- Healthy BMI range
- 59.9 to 80.7 kg
- The four disagree by several kilograms, and that spread is the honest answer. All of them come from height alone, so none knows anything about your build.
- They were devised for medical dosing rather than for telling anyone what to weigh, which is worth knowing before treating any of them as a target.
- The healthy BMI range is wider than any of the formulas and is the more useful guide for most people, because it is a range rather than a point.
About ideal weight formulas
These formulas were not written to tell anyone what to weigh. Devine's, the oldest of the four, was published in 1974 to calculate drug dosages, and the others are refinements of it for the same purpose. They spread into fitness culture as targets, which was never their job.
On a 180cm man they give 71.5, 72.6, 75.0 and 77.3 kilograms — a spread of nearly six kilos between the lowest and the highest. None is more correct than the others. If four published formulas cannot agree within six kilos, no single number from any of them deserves to be treated as a target.
All four share the same blindness: they take height and sex and nothing else. Two people of identical height can differ enormously in frame size and muscle, and the formulas cannot see either. A muscular athlete will come out "overweight" by all four and be nothing of the sort.
The healthy BMI range is the more useful comparison, and it is deliberately shown alongside them. For 180cm it runs from about 60 to 81 kilograms — a range rather than a point, which is a more honest shape for the answer. Body fat percentage and waist-to-height say more still.
What it works out
- Robinson, Miller, Devine and Hamwi formulas
- The healthy BMI weight range for your height
- Kilograms and pounds
The formula
Devine: 50kg + 2.3kg for each inch over 5 feet (45.5kg for women)
All four share this shape: a base weight at five feet, plus a fixed amount for every inch above it. They differ only in the two constants.
Devine starts at 50kg for men and adds 2.3kg an inch. At 180cm — 10.87 inches over five feet — that is 50 + 25.0, or 75.0kg. Robinson starts higher at 52kg and adds less at 1.9, giving 72.6. Miller and Hamwi land at 71.5 and 77.3.
Notice what the structure implies: every inch of height is worth exactly the same, and below five feet the formulas simply stop. Both are obviously wrong as descriptions of human bodies. They were built to be simple enough for a clinician to do in their head when calculating a drug dose, and they succeed at that.
The healthy BMI range for the same height runs from 59.9 to 80.7kg, which contains all four figures with room to spare. That range is a better answer, because being a range is a more honest shape for it.
- Base weight
- The formula's starting point at five feet. Differs by formula and by sex.
- Per inch
- What each inch above five feet adds. Between 1.36 and 2.7kg depending on the formula.
- BMI range
- The weights that put your height between a BMI of 18.5 and 24.9.
A worked example
A man of 180 centimetres.
That works out to 74.1 kg.
- Robinson
- 72.6 kg / 160.2 lb
- Miller
- 71.5 kg / 157.7 lb
- Devine
- 75.0 kg / 165.3 lb
- Hamwi
- 77.3 kg / 170.5 lb
- Healthy BMI range
- 59.9 to 80.7 kg
Questions
What is my ideal weight?
There is no single figure. For a 180cm man the four common formulas give between 71.5 and 77.3 kilograms, and the healthy BMI range is wider still at roughly 60 to 81. Anywhere in that range is defensible depending on your build.
Why do the formulas disagree?
They were derived independently from different populations for slightly different purposes. Since all four take only height and sex, the disagreement is really a measure of how much a formula that simple can be expected to know.
Which formula is best?
For their original purpose — drug dosing — Devine remains the most used. For deciding what to weigh, none of them, because none accounts for frame size, muscle or body composition.
Do these work for athletes?
Badly. A muscular athlete will read as overweight by every one of them and by BMI too. Body fat percentage is the number that separates muscle from fat, and it is the one to use instead.
Should I use ideal weight or BMI?
BMI, if you are choosing between the two, because it gives a range rather than a point and a range is more honest. Better still is waist-to-height ratio, which is the only one of the three that knows where the weight sits.
Do these apply to children?
No. Children are assessed against age-and-sex percentile charts, which is a clinical judgement rather than a calculation, and nothing on this site attempts it.
What about frame size?
None of these formulas account for it, which is one of their main limitations. Wrist circumference and elbow breadth are sometimes used to adjust the result, and the adjustments are themselves rough.