For most women, an "ideal weight" is the body weight a height-based equation or population health band says is statistically normal — not a personal target set by a doctor. The most widely quoted equations for women are the Devine, Robinson, Miller and Hamwi formulas, each one a twentieth-century expert's line of best fit for adult women of average build. Every formula works the same way: a base weight assigned to a woman who is exactly 5 feet (152 cm) tall, plus a fixed amount of weight added for every inch above that. The numbers differ because each author fitted a different dataset to a different purpose — Devine (1974) was designed to help estimate medication doses, Hamwi (1964) to plan nutrition, and Robinson and Miller (both 1983) reworked Devine's numbers against fresh data. Side by side with those formulas sits the standard healthy weight range, which comes from the body mass index (BMI) band the WHO treats as normal (18.5 to 25) and translates the same height into an actual weight range rather than a single point. All of these are reproduced instantly by the Ideal Weight Calculator the moment you pick a height unit and enter the number.
Why "ideal weight" is sex-specific
The four formulas inside the calculator all treat sex as a key input, and the reason is straightforward: at any given height, women on average carry less muscle mass and a higher proportion of essential fat than men, so the weight their bodies need is lower. Rather than build one universal equation, each of the four authors used different population data and arrived at different baseline weights for women. The calculator keeps that history intact and shows every formula's answer at once, so you can see the natural spread between them for a particular height rather than having to pick one and pretend the others do not exist.
It is worth remembering what "ideal" means in this context. None of the four authors set out to define beauty, fitness or a personal goal weight. Devine's 1974 formula was built to help clinicians estimate safe medication doses, Hamwi's 1964 formula came out of nutrition work, and Robinson and Miller both reworked Devine's numbers against new data in 1983. They are practical estimation tools, not body-image standards, and the calculator frames them the same way.
The four formulas behind the calculator
| Formula | Year | Original purpose | Tendency for women |
|---|---|---|---|
| Devine | 1974 | Estimating safe medication doses | Most widely quoted in clinical settings; sits in the middle of the range |
| Hamwi | 1964 | Planning nutrition needs | Tends to give the highest figure of the four |
| Robinson | 1983 | Re-fitted Devine against new data | Generally sits a little lower than Devine |
| Miller | 1983 | Re-fitted Devine against new data | Tends to give one of the lowest figures |
Every formula follows the same shape: a baseline weight for a woman who is exactly 5 feet (152 cm) tall, plus a fixed amount of weight added for every inch above that. The four authors chose different baselines and different per-inch slopes, which is why the calculator ends up showing four distinct numbers for any single height. A taller woman sees a wider spread between the formulas than a shorter one, because the per-inch differences compound with height. Female versions of all four use lower baseline weights than the male versions, and the calculator handles the switch automatically once you pick the female option.
Why the four formulas give different answers
Two different women with the same height can therefore get noticeably different "ideal" numbers from the calculator, and that gap is the most important thing to understand before you act on any of them. It happens for two reasons, both visible in the way the formulas are built.
The first is the baseline weight. Each author chose a different starting weight for a 5-foot woman, ranging from a leaner figure to a more substantial one. Because those starting weights are all different, the four answers already begin to diverge at 5 feet before any per-inch term is added. The second reason is the per-inch slope. Once a formula has chosen its baseline, each inch above 5 feet adds another fixed amount of weight, and that slope varies from formula to formula as well. Two formulas that start close together can still drift apart as height grows, and two that start far apart can stay closer than expected if their slopes compensate.
This is also why the spread between the formulas widens with height. At around 5 feet 3 inches (about 160 cm) the four answers usually sit within a few kilograms of each other; at around 5 feet 9 inches (about 175 cm) the gap is much wider, and the top and bottom numbers are noticeably farther apart than they are at shorter heights. The calculator lays the four answers out side by side so you can read the spread for your own height instead of guessing.
How to use the calculator step by step
- Open the Ideal Weight Calculator and choose your sex — for this article's topic, pick the female option.
- Select the height unit that matches how you measure yourself: centimetres, inches, or feet plus inches.
- Type your height into the field. In feet-plus-inches mode, fill in both boxes — feet on the left, inches on the right.
- Read the result below the input. The calculator reports all four formulas side by side, their average, and the WHO healthy BMI range, with every figure shown in both kilograms and pounds. It updates the moment your height changes, so there is no button to press.
Nothing is uploaded, and the calculation runs the moment you change a value, which means you can experiment with different heights — or compare the female and male outputs back to back — without any data leaving the page.
Reading the healthy BMI range alongside the formulas
The healthy BMI range shown next to the four formulas is not another equation — it is the standard body mass index band the WHO treats as the normal weight range, a BMI of 18.5 to 25. The calculator multiplies each end of that band by your height in metres squared, which turns a BMI range into an actual weight range in kilograms or pounds.
For a woman who is 165 cm tall (about 5 ft 5 in), the calculation works out as follows: 18.5 × 1.65² ≈ 50.4 kg at the lower end, and 25 × 1.65² ≈ 68.1 kg at the upper end. That gives a healthy range of roughly 50.4 to 68.1 kg, or about 111 to 150 lb. The BMI range is usually the most useful figure on the page: it is a band rather than a single target, and it is grounded in population health data rather than a mid-20th-century rule of thumb.
What the formulas cannot see
Every one of these formulas takes only height and sex as inputs, which means three things that matter a great deal for any individual woman are invisible to them: muscle mass, bone and frame size, and the actual body fat percentage she carries. A lean, muscular athlete can weigh well above her "ideal" number and still be in great health, while a small-framed woman with light bones can sit comfortably below it. The formulas also do not see age, ethnicity, pregnancy or any medical condition, so women whose circumstances fall outside the original study populations may find the equations drift further from their real situation.
There is one more practical limit worth knowing. Each formula was calibrated for adults of 5 feet and taller; below that height the per-inch addition has nothing to add, so the formulas collapse to their baseline value and stop being meaningful. The calculator flags this and points you to the BMI range instead. It also assumes a binary male-or-female input and does not apply to children. If you want to pair the result with an estimate of daily energy needs, the related limits of those equations are laid out in How to Calculate BMR for Women: Formula and Limits.
Beyond the number: what to do with the result
Treat the calculator output as a rough, informational estimate — not a diagnosis and not a target set by a professional. The real value of seeing four formulas alongside the BMI range together is that it tells you where your weight sits relative to a sensible band rather than nailing you to a single number, so walk into a conversation with a doctor or registered dietitian already holding that range. Pair it with related body measurement tools — a bra size calculator, a clothing size converter or an age calculator — if you want to explore the wider picture of how your body compares to standard reference figures.