Ideal Weight Calculator

“Ideal body weight” (IBW) is a single target weight estimated from height and sex. It was invented for medicine, not dieting: the Devine formula was published in 1974 to standardise how much gentamicin a patient should receive. Four formulas are in common clinical use, and this tool reports all of them plus their average, because none is the one true answer — they simply disagree by a few kilograms.

The four formulas

Every formula shares the same shape. Convert height to inches (1 inch = 2.54 cm), take over = inches − 60 (how far you are above 5 ft), then apply a base weight plus a per-inch increment:

• Devine 1974 — male 50 + 2.3 × over; female 45.5 + 2.3 × over
• Robinson 1983 — male 52 + 1.9 × over; female 49 + 1.7 × over
• Miller 1983 — male 56.2 + 1.41 × over; female 53.1 + 1.36 × over
• Hamwi 1964 — male 48 + 2.7 × over; female 45.5 + 2.2 × over

The differences are not arbitrary. Hamwi (1964) came out of diabetes dietetics and has the steepest slope, 2.7 kg per inch for men, so it returns the highest number for tall people. Miller (1983) has the flattest slope, 1.41 kg per inch, so it is the most generous at short heights and the most conservative at tall ones. Devine and Robinson sit between them. At 175 cm the four answers span roughly 68.7 kg to 72.0 kg — a 3.3 kg spread — and that spread widens the further you get from 5 ft in either direction. Reporting the average, as this tool does, is a way of saying that the real answer is a range.

Why there is no age input

None of the four formulas contains an age term, and neither does BMI. Height and sex are the only inputs, which is why a 25-year-old and a 55-year-old of the same height get the same target. Age still matters in two ways. Under about 18, height is still changing and adult formulas do not apply — paediatric practice uses growth charts and age-based dosing instead. After about 60, vertebral compression costs most people a centimetre or two of height, which raises measured BMI without a single gram of weight gain, so it is worth re-measuring rather than reusing an old figure.

Heights below 5 ft, and self-checking

For heights below 5 ft the same coefficients are applied with a negative over (standard clinical extrapolation), and the tool flags that estimates are least reliable at extremes of height. At 140 cm, for instance, Devine returns 38.8 kg — arithmetically correct but well outside the range the 1974 regression was fitted on. Inputs are bounded at 120–230 cm and 25–300 kg so that a typo cannot produce a confident-looking nonsense figure. The numbers are computed two independent ways — once via the inch conversion and once with an algebraically-rearranged per-centimetre coefficient — so the Devine value is self-checked on every run.

Measuring your height accurately

Every figure on this page is driven by a single input, so an error in your height propagates straight through to the answer. One centimetre is worth about 0.9 kg on the Devine result and roughly 0.6 kg on each end of the WHO band. Most people are one to three centimetres out, because they are quoting a number from a school medical card or a self-reported line on a form rather than a measurement taken recently.

Measure without shoes, heels and back flat against a wall, feet together, looking straight ahead so the chin is level — tilting the head back adds a centimetre or more. Hold a flat object level on the crown of the head, mark the wall, and measure from the floor with the tape vertical. Time of day matters more than people expect: spinal discs compress under load, so most adults measure around a centimetre shorter in the evening than on waking. Pick one time and stay with it rather than taking the flattering reading.

Two cases sit outside this method. If the person is under 18, height is still changing and neither the adult formulas nor the adult BMI band applies — the child height predictor estimates adult height from the parents’ heights instead. And if standing straight is not possible — scoliosis, contracture, amputation — height-based formulas need a clinical substitute such as knee height or demi-span, taken from a dietetics reference rather than from this page.

The WHO healthy band, BMI and adjusted body weight

The healthy-weight band is separate. It comes from the WHO BMI classification: a healthy BMI is 18.5–24.9, so for height h in metres the band is 18.5 × h² to 24.9 × h² kilograms. Unlike the IBW formulas it does not depend on sex, and it is a range rather than a point — usually a 15–20 kg window for an adult. The averaged ideal weight normally lands in the lower half of that window, which surprises people who expect the two methods to agree exactly. If you want the BMI side on its own, with the Asian cut-offs discussed below, use the Sri Lanka BMI calculator.

If you enter your current weight, the tool also computes your BMI (weight ÷ h²), your weight as a percentage of the Devine IBW, and your adjusted body weight (ABW): ABW = IBW + 0.4 × (actual − IBW). ABW is the figure clinicians use to dose weight-based drugs when a patient weighs more than their ideal weight, so the full dose is not driven by fat mass. The 0.4 factor is the standard convention: roughly 40% of excess body mass is treated as contributing to the volume of distribution. ABW is only meaningful when actual weight exceeds IBW — below that the tool marks it as not applicable rather than returning a number that would under-dose. For drugs dosed per square metre instead of per kilogram, the body surface area calculator covers the Mosteller and Du Bois equations. This page is educational and is not a substitute for professional medical or dosing advice.

The table below is generated by the same functions that power the calculator, so it always matches. “Ideal weight” is the average of the four formulas; the healthy range is the WHO band of BMI 18.5–24.9 at that height, which applies to both sexes. Read it as a reference point, not a pass/fail line — most people sit a few kilograms either side of the averaged figure and are perfectly healthy.

Imperial heights are rounded to the nearest half-inch, so the metric column is the exact one. For a height between two rows, enter it in the calculator above rather than interpolating by eye — the per-inch increments are not the same for men and women in three of the four formulas.

An ideal-weight figure is a height-and-sex regression, nothing more. It has no way to see what your weight is made of, and three limitations matter enough to state plainly.

Muscle reads the same as fat. Neither BMI nor any of the four formulas can separate lean mass from fat mass, so a trained rugby, athletics or gym-going adult can land above the healthy band while carrying low body fat. If your weight is above the band but your waist measurement and body-fat percentage are normal, the formula is what is wrong, not you. Estimate body fat separately with the body fat percentage calculator and use waist circumference as the tie-breaker.

Where the fat sits matters more than the total. The WHO expert consultation for Asian populations (Lancet, 2004) kept 18.5–24.9 as the international standard but added public-health action points at BMI 23 and 27.5, because South Asian adults carry more body fat — and more of it around the abdomen — at any given BMI than the populations these formulas were fitted on. A BMI of 23.5 that reads as comfortably healthy on this page is worth pairing with a waist check — the waist-to-height ratio calculator uses the simple “keep your waist under half your height” rule, which catches abdominal fat that a weight-only figure misses entirely.

A target weight is not a plan. Knowing you are 6 kg above the band says nothing about how many calories that represents. Daily energy need scales with weight, height, age and activity, so work it out from your own numbers with the TDEE calorie calculator rather than assuming a generic 2,000 kcal. If the reason you are here is drug dosing rather than diet, the clinical IBW calculator presents the same four formulas with the dosing workflow first.

• StatPearls / NCBI Bookshelf — “Ideal Body Weight” (Devine formula + ABW convention)
• Robinson JD et al., Am J Hosp Pharm 1983 — Robinson IBW formula
• Miller DR et al., Am J Hosp Pharm 1983 — Miller IBW formula
• World Health Organization — healthy BMI band (18.5–24.9)
• WHO Expert Consultation, Lancet 2004;363:157–63 — appropriate BMI for Asian populations (action points 23 and 27.5)

Formula coefficients and the WHO band were last cross-checked against these sources on 2026-06-09. The Hamwi formula originates in Hamwi GJ, “Therapy: changing dietary concepts,” in Diabetes Mellitus: Diagnosis and Treatment (American Diabetes Association, 1964); the Devine formula in Devine BJ, Drug Intell Clin Pharm 1974;8:650–655.