โ๏ธ Ideal Weight Calculator
Find your healthy weight range using 5 scientific formulas
Why the Four Formulas Fan Apart
At common adult heights the four formulas usually sit no more than about 8 kg apart. What pulls them apart is the per-inch increment. For men, Hamwi adds 2.7 kg for every inch above 5 feet, Devine 2.3, Robinson 1.9 and Miller 1.41, so the gap grows as height moves away from roughly 165โ170 cm. At 160 cm the four answers are about 4.3 kg apart, and at 190 cm they span 10.9 kg. At 220 cm, the top of the calculator's range, they run from 93.7 kg (Miller) to 119.9 kg (Hamwi), a 26 kg spread against a healthy BMI band about 31 kg wide.
The order changes with height too. For men, Devine, Hamwi and Robinson all return 61.5 kg at exactly 165.1 cm. Below that height Hamwi gives the lowest answer and Miller the highest. Hamwi and Miller swap places at 168.5 cm for men and 175.7 cm for women. By 175 cm the men's order has fully reversed: Hamwi is highest and Miller lowest. No formula is the lenient one at every height.
Two Regressions and One Rule of Thumb
Devine's equation appeared in 1974, in a gentamicin case study in Drug Intelligence and Clinical Pharmacy. In 2000, Pai and Paloucek reviewed these equations in the Annals of Pharmacotherapy. They traced them to height-weight tables built to compare populations and correlate weight with mortality, and found that later regression-based refinements of Devine's equation kept landing close to his original figures.
Robinson's team took the regression route in a 1983 paper in the American Journal of Hospital Pharmacy, fitting median weight against height in Metropolitan Life Insurance tables. It judged the older empirical method probably only slightly in error, but still recommended data-derived formulas for some drug dosing. The published coefficients were 51.65 kg + 1.85 kg per inch for men and 48.67 kg + 1.65 kg for women. The calculator uses the commonly quoted rounded forms, 52 + 1.9 and 49 + 1.7. Later that year, Miller and colleagues proposed their own equations in the same journal, with a higher base and a shallower slope. That shape makes Miller generous for shorter adults and strict for taller ones.
Pai and Paloucek concluded that the equations look alike because the tables behind them broadly agree, and that any one of them can be used. Those tables described insured policyholders, not a representative sample. Hospitals keep Devine because dosing needs one consistent lean-weight estimate, often adjusted to IBW + 0.4 ร (actual weight โ IBW) in obesity. It is a dosing tool, not a personal weight target.
When the Standard Ranges Need Context
One factor is ancestry. A WHO expert consultation, published in The Lancet in 2004, found that BMI, body fat and health risk relate differently in Asian populations than in European ones, and that a substantial share of Asian people are at high risk of type 2 diabetes and cardiovascular disease below a BMI of 25. The consultation kept the international categories and added action points at 23.0, 27.5, 32.5 and 37.5 kg/mยฒ. It set no single Asian cut-off, because the level where observed risk began to rise varied from 22 to 25 kg/mยฒ between populations, leaving each country to define risk for its own population.
Another is short stature. All four formulas count inches above 5 feet, so below 152.4 cm the height term turns negative and the results diverge quickly. For a woman at 145 cm, Devine gives 38.8 kg, just under the 38.9 kg lower edge of the BMI range, while Miller gives 49.1 kg โ about 10 kg apart, so treat formula figures cautiously here.
The lower bound matters too. The Global BMI Mortality Collaboration's 2016 Lancet meta-analysis drew on 239 prospective studies. Its main analysis narrowed to 189 of them, covering 3.9 million never-smokers with no reported chronic disease at recruitment and still followed five years later. All-cause mortality was minimal across BMI 20.0โ25.0, and 13% higher at BMI 18.5 to 20 than in the 22.5โ25.0 reference band. The healthy range and the lowest-mortality range share a top but not a bottom. At 175 cm, BMI 18.5 is 56.7 kg, about 4.6 kg below the BMI-20 weight of 61.3 kg.