The classic ideal body weight formula works like this: take a base weight for someone who is exactly 5 feet tall, then add a fixed number of kilograms for every inch of height above that baseline. For a male, Devine's 1974 formula uses a 50 kg baseline plus 2.3 kg per inch over 5 ft, Hamwi's 1964 formula uses a 48 kg baseline plus 2.7 kg per inch, Robinson's 1983 formula uses 52 kg plus 1.9 kg, and Miller's 1983 formula uses 56.2 kg plus 1.41 kg. Female versions of the same formulas use lower base weights and smaller per-inch increments, which keeps the four results on a comparable scale. Four formulas exist because no single definition of "ideal" weight has ever been universally agreed, and each was built for a different original purpose, from medication dosing to nutrition planning. The fastest way to apply all four at once is the Ideal Weight Calculator, which takes your height and sex, runs the math instantly in your browser, and prints every result in both kilograms and pounds alongside a healthy BMI range.
The Four Classic Ideal Weight Formulas and Where They Came From
Every formula in regular clinical use follows the same simple pattern: a baseline weight at exactly 5 feet (152 cm), plus an extra amount for every inch (2.54 cm) you stand above that. The four that show up most often all came out of work in the second half of the 20th century, but each was designed for a different job.
Hamwi (1964) was published by Dr. G.J. Hamwi to help estimate nutrition needs, which is why its per-inch slope is steep — it generally produces the highest of the four numbers. Devine (1974) was introduced by Dr. B.J. Devine as a way to calculate medication doses and has since become the most widely quoted formula in clinical settings. Robinson (1983) and Miller (1983) both reworked Devine's starting points and slopes against fresher population data and tend to sit a little lower. All four use a binary male or female input and apply the math only to adults 5 feet and taller.
How to Calculate Your Ideal Weight in Three Steps
- Open the Ideal Weight Calculator in a browser tab and choose your sex from the two options at the top.
- Pick a height unit — centimeters, inches, or feet plus inches — then type your height. In feet-plus-inches mode, fill in both the feet box and the inches box so the height reads correctly.
- Read your ideal weight from all four formulas, their average, and the healthy BMI range below — the results update the moment you type, in both kg and lb, with no button to press and nothing uploaded.
Because the calculation runs entirely in your browser, there is no save button and no sign-up to worry about. If you want to see how the same height plays out under different assumptions, switch the sex and the height value and watch all four formulas update at once.
Why the Four Formulas Give Different Numbers
The reason you see four results side by side is that there is no single agreed "ideal" weight. Each formula is a different researcher's line of best fit, fitted to a different dataset, and the slopes and baselines reflect those choices.
| Formula | Year | Base weight at 5 ft (men) | Per inch above 5 ft (men) | Original purpose |
|---|---|---|---|---|
| Hamwi | 1964 | 48 kg | 2.7 kg | Nutrition planning |
| Devine | 1974 | 50 kg | 2.3 kg | Medication dosing |
| Robinson | 1983 | 52 kg | 1.9 kg | Population re-fit |
| Miller | 1983 | 56.2 kg | 1.41 kg | Population re-fit |
Because their slopes and starting points differ, a tall person sees a wider spread between the formulas than a short person does. For a moderately tall adult the four results cluster fairly tightly, but for someone well over 6 ft the gap between Hamwi and Miller can be 10 kg or more. Female versions of the same formulas use lower base weights and slightly lower per-inch increments, so the same pattern appears at a smaller scale.
The Healthy BMI Range vs. a Single "Ideal" Number
The healthy range shown next to the four formulas is not a formula at all but a band from body mass index. BMI is weight divided by height squared, and health bodies such as the WHO treat 18.5 to 25 as the normal range for adults. Multiplying each end of that band by your height in metres squared turns it into an actual weight range. For a 175 cm (1.75 m) person, for example, the BMI range works out to 18.5 × 1.75² ≈ 56.7 kg at the lower end and 25 × 1.75² ≈ 76.6 kg at the upper end. This range is usually more informative than any single "ideal" number because it is a range rather than one target, and it is grounded in population health data rather than a mid-20th-century rule of thumb. The calculator displays this BMI range alongside the four formulas so you can read both at once.
What These Formulas Cannot Tell You
Every formula on this page takes only height and sex, so it cannot see anything else about you. That has a few predictable consequences.
- No muscle versus fat discrimination. A lean, muscular athlete can weigh well above their "ideal" number and still be perfectly healthy; the reverse can also be true.
- No frame size adjustment. Someone with a very light frame can be comfortable at the low end of the band, while a heavier-framed person may sit naturally higher.
- No ethnicity, age, or medical history input. Population studies show healthy BMI bands vary modestly between groups, but the formulas do not model that.
- Below 5 ft the math collapses to the baseline value and stops being meaningful. The calculator flags this and points you to the BMI range instead.
- Binary sex input only — these formulas were not designed for children or for use during pregnancy.
When to Use Which Number
For most readers, the most useful single output on the page is the healthy BMI range, because it is a band rather than a single point and is tied to a widely accepted health standard. The four formula numbers are most useful when you want to compare yourself to a specific clinical reference — Devine for medication dosing context, Hamwi for a historical nutrition reference, Robinson and Miller for a more modern population fit. Look at the average of all four plus the BMI band together, and you will have a sensible zone your weight could fall in. For a deeper look at how height and weight interact, a quick check with the height-and-weight BMI walkthrough can help you see how the same range is built from scratch.
Treat every number as a rough, informational estimate. These formulas are useful for a starting conversation with a doctor or a registered dietitian, not as a hard target on their own.