Ideal Weight Calculator

How to Use the Ideal Weight Calculator

There is no such thing as one ideal weight, and the most useful thing this calculator does is show you why. It runs four published formulas side by side, and they disagree — by nearly five kilograms at an average adult height. That disagreement is the finding, not a flaw in the arithmetic.

1. Set your units and enter your height. Every one of these formulas is built on height alone, so this single measurement drives all four answers. Measure without shoes, standing straight, heels together.
2. Select sex at birth. Each formula carries a separate base weight and per-inch increment for men and women, drawn from the population the authors studied.
3. Add your current weight if you want context. It is optional. With it, the table shows how far each formula sits from where you are, and the tiles show your BMI.
4. Read the range rather than the average. The headline figure is the mean of the four, which is convenient but slightly false in its precision. The healthy BMI band underneath it is wider and more honest.

Nothing you type is sent anywhere. The arithmetic happens in your browser, the page makes no network request while you use it, and there is no account to create.

Ideal Weight Formulas

Every formula on this page shares one shape. Each starts from a base weight at five feet and adds a fixed amount for every inch above that. Only the two constants change, which is why the four answers stay in the same neighbourhood without ever agreeing.

The increment is where the four part company. Hamwi adds 2.7 kg per inch for men, Miller only 1.41 — nearly double. At five foot ten that gap has compounded over ten inches, and the answers separate by almost five kilograms. Below five feet the formulas have nothing left to work with, because there is no negative-inch case they were built to handle, and the calculator refuses rather than extrapolating.

The BMI range is a different kind of statement. It does not produce a single weight at all; it produces a band, and at any adult height that band is roughly twenty kilograms wide. That width is not vagueness — it reflects how much healthy variation in build genuinely exists at a given height.

Example

Worked example one: a man of 178 cm. That is 70.078740 inches, which is 10.078740 inches above five feet. Devine gives 50 + 2.3 × 10.07874 = 73.18 kg. Robinson gives 52 + 1.9 × 10.07874 = 71.15 kg. Miller gives 56.2 + 1.41 × 10.07874 = 70.41 kg. Hamwi gives 48 + 2.7 × 10.07874 = 75.21 kg.

The mean of those four is 72.49 kg, or 159.8 lb, and they span 4.80 kg from Miller at the bottom to Hamwi at the top. Meanwhile 1.78 m squared is 3.1684, so the healthy BMI band runs from 18.5 × 3.1684 = 58.62 kg to 24.9 × 3.1684 = 78.89 kg — a range 20.28 kg wide, more than four times the disagreement between the formulas.

At an actual weight of 82 kg, BMI is 82 ÷ 3.1684 = 25.88, which sits just above the healthy band. The formulas would each suggest a loss of between 6.8 and 11.6 kg, and the BMI band would suggest 3.1 kg. Those are very different pieces of advice from the same height.

Worked example two: a woman of 165 cm. That is 64.960630 inches, 4.960630 above five feet. Devine gives 45.5 + 2.3 × 4.96063 = 56.91 kg, Robinson 49 + 1.7 × 4.96063 = 57.43 kg, Miller 53.1 + 1.36 × 4.96063 = 59.85 kg and Hamwi 45.5 + 2.2 × 4.96063 = 56.41 kg. The mean is 57.65 kg and the spread is 3.43 kg.

Notice that the ordering has changed. At 178 cm Hamwi read highest and Miller lowest; at 165 cm for a woman the order reverses, because Miller starts from a much higher base and climbs slowly while Hamwi starts low and climbs fast. The two lines cross somewhere in between. Any claim that one of these formulas 'reads high' is therefore only true at particular heights.

Reading the Spread Rather Than the Average

Read the spread first. If the four formulas sit within a couple of kilograms of each other, they are telling you something reasonably consistent. If they are five kilograms apart, as they are at 178 cm, then the concept itself is doing less work than it appears to and the healthy band is the better guide.

Then read the band. A twenty-kilogram healthy range at a given height is not a failure of precision — it is the accurate description of how much variation in frame, muscle and build exists among healthy adults of the same height. Someone at the bottom of that band and someone at the top can both be perfectly well.

Where you sit within the band matters far less than most people assume. Across large population studies, mortality risk is close to flat through the middle of the healthy range and rises only towards the extremes. Moving from BMI 22 to BMI 21 is not a health intervention; moving from 31 to 27 usually is.

The single most useful cross-check is composition rather than weight. Two people at the same height and the same 82 kg can have entirely different amounts of fat and muscle, and every formula on this page would give them identical advice. The body fat calculator separates those two, and the BMI calculator shows where the weight-and-height view puts you.

If a number here is far from your current weight, treat it as a prompt to ask why rather than as a target to hit. A powerlifter and a distance runner of the same height should not weigh the same, and neither should match a 1974 dosing table.

Five Limits Worth Knowing

Five things worth knowing before you take any of these figures seriously.

They were built for medicine, not health. Devine's formula appeared in a 1974 note about gentamicin dosing. Its purpose was to give clinicians a consistent weight for calculating drug volumes in patients whose real weight would distort the dose. Nobody validated it as a target for the general public, and it has been used that way ever since largely by accident.

They ignore frame size entirely. Two people of identical height with visibly different skeletal builds get identical answers. Older clinical practice adjusted by roughly 10% up or down for large or small frames, measured at the wrist or elbow, and that adjustment is larger than the disagreement between the formulas themselves.

They ignore muscle completely. Height is the only input. A well-trained athlete will exceed every figure here while carrying less fat than someone who matches them exactly, which is the clearest possible demonstration that a weight target is a poor proxy for a health target.

The populations were narrow. The samples behind these equations were mostly white, mostly American or European, and mostly from the middle of the twentieth century. Body composition at a given BMI varies measurably between populations, and several health bodies now use different BMI thresholds for South Asian and East Asian populations for exactly this reason.

Below five feet they do not apply. Every formula begins at a sixty-inch base and adds from there. Extrapolating downwards produces answers that look plausible and mean nothing, so this calculator declines rather than guessing. For children and adolescents, weight is assessed against growth percentiles instead, and no adult formula is appropriate.

Used well, the output here is a rough orientation and a reminder of how much honest disagreement exists. Paired with the calorie calculator for intake and the TDEE calculator for expenditure, it gives you a sense of direction — which is all it was ever able to give.