Ideal Weight Formulas Compared: Devine, Robinson, Miller and Hamwi

Ask the internet what you should weigh and you will get several confidently different numbers. That is not because one source is wrong; it is because there are multiple established formulas, they were derived from different data for different purposes, and they genuinely disagree.

The Ideal Weight Calculator shows all four side by side precisely so the disagreement is visible rather than hidden. A spread of five or six kilograms between them is normal, and that spread is itself the most useful thing the calculation tells you.

None of them was designed to help you set a weight-loss goal. The Devine formula, published in 1974, was created to calculate drug dosages — several medications are dosed on lean body mass, and clinicians needed a quick estimate from height alone.

Hamwi's formula (1964) came out of diabetes care, as a rapid bedside method for estimating nutritional needs. Robinson (1983) and Miller (1983) were later attempts to fit the same idea more closely to actual measured population data, both explicitly presented as refinements of Devine.

They share a structure: a base weight at five feet of height, plus a fixed increment for each additional inch. That structure is what makes them fast, and also what limits them.

All four are expressed in kilograms, with height in inches above five feet. The differences in both the base and the per-inch increment are what produce the spread.

Notice that the formulas with the lowest base weights have the steepest per-inch increments. Hamwi starts lowest for men and climbs fastest; Miller starts highest and climbs slowest. The practical consequence is that they agree most closely near five feet and diverge as height increases.

For a tall person the spread can exceed eight kilograms, which is a substantial disagreement about something being presented as an 'ideal'. For someone of average height it is typically three to five kilograms.

That divergence is a feature of the underlying data, not an error. Each was fitted to a different sample, using different methods, at a different time, for a different purpose. Averaging them — which the calculator also shows as a consensus estimate — is a reasonable way to avoid over-committing to any single one's particular bias.

Every one of these formulas takes exactly two inputs: height and sex. That is a striking amount of information to leave out.

The healthy-BMI weight range is a better practical tool for most purposes. Taking the WHO normal range of 18.5 to 24.9 and multiplying by height squared gives a window rather than a point — and a window is a more honest representation of the underlying reality.

The Healthy Weight Calculator does exactly this and, unlike the ideal-weight formulas, it also tells you how far you are from the nearest boundary if you fall outside it. Being anywhere within that window, at a stable weight, with reasonable habits, is a perfectly good outcome.

For anyone who trains seriously, body fat percentage is more informative still. A muscular person can sit above every ideal-weight formula and above the healthy-BMI window while carrying genuinely low body fat, and in that case the weight figures are simply the wrong instrument.

The standard objection to any height-based weight formula is frame size, and it is a fair one. Skeletal dimensions vary substantially between people of identical height, and a broader frame carries more bone and more muscle attachment area without any excess fat.

The traditional workaround was to measure wrist circumference or elbow breadth and classify people as small, medium or large framed, adjusting the target by roughly 10% in each direction. Those adjustments come from mid-twentieth-century insurance tables and have never been particularly well validated, but the underlying point stands: a single number derived from height alone cannot possibly fit everyone.

In practice, a simpler response works better than a frame correction. If you are lean by body fat percentage and your waist measurement is unremarkable, your weight is fine regardless of what a 1974 formula says about it.

It is worth saying clearly that these formulas are not junk. They remain in active clinical use, and for their original purpose they work well: estimating a reference body weight quickly when calculating drug doses, ventilator tidal volumes or nutritional requirements.

In those settings the alternative is not a better formula — it is no estimate at all, or a delay. A quick approximation from height and sex is genuinely valuable when a clinician needs a lean-mass proxy immediately and cannot weigh an unconscious patient.

The mistake is not the formulas; it is transplanting them from that context into personal weight goals, where the questions being asked are entirely different and where far better tools exist.

Fixating on one precise figure tends to be counterproductive. It converts a broad range of healthy outcomes into a pass/fail test, and it invites the conclusion that being two kilograms above an arbitrary formula's output constitutes failure.

It also ignores that healthy weight is not static. Body composition, and reasonable weight, change across a lifetime. A figure derived from 1970s clinical dosing tables has no particular claim to being your correct weight at 55.

A more useful framing: identify a range you can maintain without constant restriction, where your energy is good, your training progresses, and your blood markers are healthy. That is a target worth having.

Use the ideal-weight formulas as historical reference points and as a rough sanity check — that is what they are good for, and it is close to what they were built for. Their genuine value is showing you a plausible range, not a destination.

For setting an actual goal, the healthy-BMI window is a better starting point, body fat percentage is better still, and how you feel and perform over months beats all of them.