Search for your ideal weight and four different formulas will hand you four different answers, sometimes six kilograms apart. None of them is wrong, exactly; they were built for different purposes, and one of them was never about health at all, it was invented to dose drugs. This guide puts Devine, Robinson, Miller, and Hamwi side by side with worked numbers, explains where each came from, and shows what to use instead of any single magic figure. Our free ideal weight calculator computes all of them at once.
In this guide
The four formulas
All four share one structure: a base weight for a height of 5 feet (152.4 cm), plus an increment per inch above it.
| Formula | Men | Women |
|---|---|---|
| Devine (1974) | 50 kg + 2.3 per inch | 45.5 kg + 2.3 per inch |
| Robinson (1983) | 52 kg + 1.9 per inch | 49 kg + 1.7 per inch |
| Miller (1983) | 56.2 kg + 1.41 per inch | 53.1 kg + 1.36 per inch |
| Hamwi (1964) | 48 kg + 2.7 per inch | 45.5 kg + 2.2 per inch |
Notice the disagreement built into the table: Hamwi starts lowest and climbs fastest, Miller starts highest and climbs slowest. Tall people get the widest spread of “ideal” answers, short people can land below some formulas’ base weights entirely, which is one of several reasons to treat all four as historical estimates rather than verdicts.
Worked examples: one man, one woman
A man of 180 cm is 70.9 inches tall, 10.9 inches over five feet:
| Formula | Result (man, 180 cm) | Result (woman, 165 cm) |
|---|---|---|
| Devine | 75.0 kg | 56.9 kg |
| Robinson | 72.6 kg | 57.4 kg |
| Miller | 71.5 kg | 59.8 kg |
| Hamwi | 77.3 kg | 56.4 kg |
The man’s four “ideals” span 5.8 kg, the woman’s (at 165 cm, five inches over five feet) span 3.4 kg. If a concept’s best four definitions disagree by the weight of a bowling ball, the concept is an estimate band, not a target. That is the correct reading, and it is liberating rather than disappointing.
Where these numbers actually come from
None of these formulas came out of large studies of health outcomes. The Hamwi rule (1964) was a clinician’s quick rule of thumb for counseling patients. The Devine formula (1974), the most famous of all, was proposed for calculating drug doses: many medications dose better against an idealized lean-ish weight than against total weight, and Devine’s estimate filled that gap. It still does; pharmacists use it today. Robinson and Miller (both 1983) are later refinements fitted against insurance height-weight tables of the era. So the most-quoted “ideal weight” on the internet is a 1970s pharmacology convenience, built on mid-century actuarial tables, for a purpose that had nothing to do with how anyone should look or feel. Useful history to remember the next time a single number on a screen carries emotional weight.
The healthier question: a range, not a point
Modern guidance avoids single-point ideals and uses ranges. The conventional healthy BMI band of 18.5 to 24.9 translates height into a weight range:
- 180 cm: 59.9 to 80.7 kg
- 165 cm: 50.4 to 67.8 kg
Notice that all four formula results above fall inside these bands; the formulas are mostly picking arbitrary points within the same territory. BMI ranges have their own well-known blind spots, muscle mass above all, which our BMI guide covers, and the BMI calculator computes in both directions. For what your weight is made of, rather than what it totals, body composition is the better question, measured cheaply with the tape-measure method in our Navy body fat guide.
How to actually use all this
- As a sanity range: run the calculator, look at the spread of all four formulas plus the BMI band, and treat the overlap as a generous reference zone, not a finish line.
- As a goal-setting aid: if you are far outside the zone, any point inside it is a defensible long-term direction; the pace of getting there matters more than the exact endpoint, and that pace is the calorie arithmetic in the BMR and calories pillar.
- Not as a judge: the formulas know your height and sex, nothing else. They do not know your frame, your muscle, your age, or your history. A muscular 85 kg at 180 cm out-healths a skinny-fat 74 kg every day of the week, and no height formula can see the difference.
Frequently asked questions
Which formula is the most accurate?
Accurate at what? For drug dosing, Devine by convention. As a health target, none has outcome evidence behind it; the BMI range plus a body-composition measure describes health far better than any single-point formula.
Why do the formulas only use height and sex?
Because they were built for speed in the 1960s to 1980s, before cheap computation. Their entire input is two facts, which is exactly why their output deserves limited authority.
What about frame size, wrist measurements and so on?
Some traditions adjust the result a few percent either way for “small” or “large” frame, usually judged by wrist circumference. It acknowledges the right problem (frames differ) with another rough patch. Measuring body composition directly answers the same question with actual data.
I am below every formula’s number. Should I gain?
Not automatically; the formulas are not minimums any more than they are targets. If you are under the healthy BMI band or your energy and health feel off, that conversation belongs with a professional, not a 1974 equation.
Is this medical advice?
No. These are reference formulas presented for general information, with their limitations spelled out. Personal targets, especially with any medical condition, should be set with qualified guidance.