Ideal Weight Calculator

Pick your sex, enter your height, and the calculator returns ideal body weight estimates from four published formulas — Devine, Robinson, Miller and Hamwi — side by side. Switch the units control to imperial to enter feet and inches and read the results in pounds; metric heights return kilograms. Showing all four at once is deliberate. The single most useful thing these formulas can tell you is how much they disagree, and a lone number would hide that.

What "ideal body weight" was actually for

None of these four formulas was ever validated as a health target. Each is a shortcut for turning a height into one reference weight in seconds, wanted for scaling a drug dose or sizing a diet rather than for setting a patient's goal. The insurance height-and-weight tables behind them do have a mortality pedigree, which is where the words desirable and ideal entered the vocabulary, but the equations themselves were fitted for arithmetic convenience, and no trial has tested whether reaching one of these numbers improves anyone's health.

The oldest of the four is G. J. Hamwi's. He set it out in 1964 in a chapter on changing dietary concepts published by the American Diabetes Association, as a bedside method for sizing the diet of a person with diabetes. Hamwi wrote it in pounds, arithmetic a physician could do from memory: a man starts at 106 lb for the first five feet of height and adds 6 lb for every inch above that, while a woman starts at 100 lb and adds 5 lb. The kilogram coefficients in the table below are the rounded conversions later sources settled on.

A decade later B. J. Devine used the same five-foot anchor and re-set its numbers. Writing in 1974 in Drug Intelligence and Clinical Pharmacy, in a piece on gentamicin therapy, Devine wanted a standard weight against which to scale doses of that antibiotic. Gentamicin distributes into lean tissue rather than fat, so dosing a heavy patient on total body weight overshoots and raises the risk of kidney and inner-ear damage. The equation — 50 kg plus 2.3 kg per inch over five feet for men, 45.5 kg on the same slope for women — was offered as a rule of thumb with no supporting data. In 2000 the pharmacists M. P. Pai and F. P. Paloucek traced it in the Annals of Pharmacotherapy to an older bedside rule already circulating from the insurance tables, rather than to any study of Devine's own. They became the default anyway. Aminoglycoside dosing and the predicted body weight that sets low tidal volumes in ARDS Network lung-protective ventilation both use Devine's coefficients unchanged.

In 1983 two re-fits appeared in the American Journal of Hospital Pharmacy: a research paper in June from J. D. Robinson and colleagues, and a letter in October from D. R. Miller and colleagues. Robinson's group regressed median weight against height on the Metropolitan Life Insurance Company tables, arguing that dosing should rest on real height-and-weight data rather than an inherited rule, while conceding the old rule's errors were probably minor. Their all-frame-size regression gave 51.65 kg plus 1.85 kg per inch for men and 48.67 kg plus 1.65 kg per inch for women, values that circulate today rounded to 52 and 1.9, 49 and 1.7. Miller's letter landed on flatter slopes still, 1.41 kg per inch for men and 1.36 for women, hung on higher bases. That is why this calculator shows four answers for one person: four sets of authors, three decades, and different reference data behind one idea.

The shared formula

All four share one algebraic skeleton — a base weight assigned at exactly five feet, plus a fixed increment for every inch above it:

IBW = base + k × (height_in − 60)

The coefficients are where they part company:

Every female base sits below its male counterpart, reflecting the lighter reference populations the authors fitted against. Bases and slopes moved in opposite directions, though: Robinson and Miller cut the per-inch increment sharply for both sexes yet raised the female base well above Devine's 45.5 kg, so the re-fits start heavier and climb more gently. Devine, Robinson and Miller wrote in kilograms while keying the step to inches, so each increment is the per-centimetre version scaled by 2.54: Devine's metric form adds 0.9 kg per centimetre above five feet, and multiplying 0.9 by 2.54 recovers the 2.3 kg per inch in the table. The calculator handles that conversion internally, so centimetres and feet-and-inches give the same underlying answer, reported to one decimal place.

A worked example

With the defaults — a man at 178 cm — height converts to 70.08 in, which is 10.08 in over five feet. Devine gives 50 + 2.3 × 10.08 = 73.2 kg. Robinson gives 52 + 1.9 × 10.08 = 71.1 kg, Miller gives 56.2 + 1.41 × 10.08 = 70.4 kg, and Hamwi gives 48 + 2.7 × 10.08 = 75.2 kg. Same person, four answers, 4.8 kg apart. The spread is not narrowest at the five-foot anchor. At exactly 5 ft the four bases are 8.2 kg apart, from Hamwi's 48 kg up to Miller's 56.2 kg. The steeper slopes then close that gap: around 5 ft 6 in the four answers converge to within roughly 1.3 kg, and only above that height do they fan out again, reaching 4.8 kg at 178 cm and about 12.4 kg at 6 ft 4 in. The estimates are tightest near average adult height and loosest at both extremes.

What the formulas leave out

Everything except height and sex. Age, muscle mass, ethnicity and body composition are invisible to them, and so is frame size in the versions used here. Robinson's paper did publish separate small, medium and large frame equations, but the all-frame version entered general use and is the one this calculator applies. A rugby lock and a marathon runner of identical height and sex therefore receive identical numbers, which is reasonable for scaling a drug dose and close to useless as a personal target. All four are published only for heights of five feet and above, stated as a base plus a step for every inch over 60, so the calculator reports an error under 152.4 cm rather than extrapolating into weights the equations were never written to produce. If a result surprises you, that reflects dosing and diet conventions fixed between 1964 and 1983 more than anything about your body.

Why a BMI range is usually the better question

A single ideal weight is a clinical convenience. The question most people are really asking — is my weight healthy for my height — is better answered by a band than a point, and that band has a longer history than any of these four formulas.

Its root is the work of the Belgian astronomer, mathematician and statistician Adolphe Quetelet, who from the 1830s studied the distribution of human measurements and found that adult weight rose roughly with the square of height. The ratio of weight to height squared became known as the Quetelet index. Quetelet was describing the average person statistically and never proposed his index as a medical yardstick. It took on that role only in July 1972, when Ancel Keys and four co-authors, writing in the Journal of Chronic Diseases, compared relative-weight measures across 7,424 men in twelve cohorts in five countries, judged the weight-over-height-squared ratio the best of them as an indicator of body fatness, and named it the body mass index.

From that index the World Health Organization settled on a healthy adult range of 18.5 to 24.9 kg/m², and the CDC in the US and the NHS in the UK publish the same band. At 178 cm it runs from about 58.6 to 78.9 kg — roughly 129 to 174 lb — a spread of more than 20 kg that comfortably contains all four formula outputs above. Pai and Paloucek reached the same caution from the other direction: because the four equations descend from the same insurance tables, any of them will serve for dosing, which is exactly why none is a personal target. Reading the four estimates as points inside that wider band, rather than treating any one of them as the goal, is the honest way to use this tool.

Ideal body weight formulas are clinical dosing references, not personal targets, so weight goals belong in a conversation with your doctor. See the site disclaimer.

Frequently asked questions

What is the ideal weight for a 5 ft 10 in man?

The four formulas disagree by design. Devine says 73.0 kg (161 lb), Robinson 71.0 kg (157 lb), Miller 70.3 kg (155 lb) and Hamwi 75.0 kg (165 lb). That 4.7 kg spread is typical, so read the results as a band rather than a single target.

Where does the Devine formula come from?

B. J. Devine published it in 1974 in Drug Intelligence and Clinical Pharmacy so that hospital pharmacists could dose gentamicin against a standard weight instead of actual weight. It was never validated as a health target, yet it remains the default ideal body weight formula in clinical medicine, including the tidal-volume settings used in mechanical ventilation.

Why do Devine, Robinson, Miller and Hamwi give different answers?

Each was fitted at a different time against different reference data. Hamwi's 1964 rule was a quick clinic heuristic, while Robinson and Miller re-fitted height-weight tables in 1983 and arrived at flatter slopes — 1.9 and 1.41 kg per inch for men against Devine's 2.3. At 178 cm the four estimates for a man span 70.4 to 75.2 kg.

Is ideal body weight the same as a healthy BMI?

No. The healthy BMI band of 18.5 to 24.9 covers 58.6 to 78.9 kg at a height of 178 cm, a range of more than 20 kg, and all four formula results land inside it. Public health bodies such as the CDC and the NHS work with that band rather than a single number.

Do ideal weight formulas work for women and shorter people?

Each formula has a separate female version with a lower base weight, and this calculator applies it automatically once you pick a sex. None of the formulas are defined below 5 ft (152.4 cm), which is why the calculator reports an error there rather than extrapolating downward into numbers the authors never intended.