Understanding your ideal weight results
Each formula was proposed by a different author for clinical use, chiefly standardizing drug doses. The table summarizes their origins; the WHO healthy-BMI range is the screening reference used by health agencies today.
| Formula | Year | Original purpose |
|---|---|---|
| Hamwi | 1964 | Quick clinical rule of thumb from diabetes practice |
| Devine | 1974 | Standardizing per-kilogram drug dosing (e.g. gentamicin) |
| Robinson | 1983 | Modification of Devine to better fit height-weight data |
| Miller | 1983 | Alternative modification with a flatter height slope |
| WHO healthy-BMI range | 2000 (TRS 894) | Population screening range, BMI 18.5–24.9 kg/m² |
- Ideal-weight formulas were developed for drug dosing and clinical convention, not as health targets; a documented history is given by Pai and Paloucek (2000).
- The formulas ignore body composition, age, ethnicity and frame size — a muscular person can be healthy well above every formula estimate.
- The four estimates commonly span several kilograms for the same height; the disagreement is a feature of the method, not an error in the calculator.
- Health agencies frame healthy weight as the range corresponding to BMI 18.5–24.9, and clinicians interpret any weight value alongside waist measurements and overall health rather than against a single number.
What is ideal body weight?
Ideal body weight (IBW) is a reference weight estimated from height and sex using simple linear formulas. The best-known equation, published by B. J. Devine in 1974, was introduced to standardize drug dosing — many medication doses are still calculated per kilogram of ideal rather than actual body weight — and was never validated as a health target.
The earlier Hamwi formula (1964) originated as a quick clinical rule of thumb for diabetes care, and the Robinson (1983) and Miller (1983) formulas were later modifications intended to better match population height-weight data. A historical review by Pai and Paloucek (Annals of Pharmacotherapy, 2000) documents that all four rest on approximation and convention rather than on outcome studies linking the computed weight to best health.
Because the formulas differ in their constants, they can disagree by several kilograms for the same person — a spread that itself illustrates that no single 'ideal' number exists. None of them accounts for body composition, age, ethnicity or frame size.
Health agencies do not define a single ideal weight. The World Health Organization instead defines a healthy BMI range of 18.5–24.9 kg/m², which translates into a weight range — not a point — for any given height. This calculator shows that range alongside the formula estimates for context.
How to use this ideal weight calculator
- Select your sex — each formula has separate male and female constants.
- Enter your height, using the Metric/Imperial toggle if you prefer feet and inches.
- Compare the four formula estimates; the spread between them reflects the approximate nature of all ideal-weight equations.
- Check the WHO healthy-BMI weight range for your height, which health agencies use for weight screening instead of a single number.
The formulas behind ideal body weight
All four equations start from a base weight at 5 feet (152.4 cm) of height and add a fixed increment per inch (2.54 cm) above that. For heights at or below 5 feet, the base weight is used. This calculator converts your height to inches internally and reports results in kilograms.
Common mistakes
- Treating a formula output as a weight-loss or weight-gain goal — the equations were designed for drug-dose standardization, not as health targets.
- Picking whichever formula gives the most flattering number; the spread between formulas simply reflects their approximate nature.
- Applying the formulas to children or teenagers — they were derived for adults, and pediatric assessment uses growth-percentile charts instead.
- Ignoring body composition: muscle mass can place a healthy person far above every formula estimate.
- Using the adult male or female constants interchangeably — each formula has sex-specific base weights and increments.
よくある質問
What is my ideal weight for my height?
There is no single scientifically defined ideal weight. Classic formulas such as Devine (1974) estimate, for example, about 68 kg for a 173 cm (5 ft 8 in) man, but different formulas give different numbers. Health agencies instead use the WHO healthy BMI range of 18.5–24.9, which for 173 cm corresponds to roughly 55–75 kg.
Why do the four formulas give different answers?
Each author chose different base weights and per-inch increments: Hamwi (1964) and Devine (1974) used steeper increments (2.2–2.7 kg per inch), while Robinson and Miller (both 1983) fitted flatter slopes to population data. Because none was validated against health outcomes, there is no basis for calling one of them correct.
What were ideal weight formulas originally for?
Mainly drug dosing. The Devine formula was proposed in 1974 so that medications dosed per kilogram — such as the antibiotic gentamicin — could use a standardized lean reference weight rather than actual weight. The Hamwi formula began as a quick rule of thumb in diabetes care in 1964. Their history is reviewed by Pai and Paloucek (2000).
Is ideal body weight the same as a healthy weight?
No. Ideal body weight is a formula convention based only on height and sex. Healthy weight, as used by the WHO and other agencies, is the range of weights giving a BMI of 18.5–24.9 kg/m², interpreted together with waist circumference, body composition and overall health by a clinician.
Do the formulas work for very short or very tall people?
Less well. The equations were built around a 5-foot baseline with a linear increment, and at heights well below 5 feet (152 cm) they simply return the base weight, while at very tall heights the linear assumption drifts from population data. The WHO healthy-BMI range scales with height squared and behaves more consistently across the height spectrum.
Does frame size or muscle change my ideal weight?
The formulas cannot account for it — they use only height and sex. A person with high muscle mass or a larger skeletal frame can weigh more than every formula estimate while having healthy body composition. Body-fat percentage, waist-to-hip ratio and clinical assessment describe such cases far better than any ideal-weight equation.
参考文献
- Devine BJ. Gentamicin therapy. Drug Intelligence & Clinical Pharmacy 1974; 8: 650–655.
- Robinson JD, Lupkiewicz SM, Palenik L, Lopez LM, Ariet M. Determination of ideal body weight for drug dosage calculations. American Journal of Hospital Pharmacy 1983; 40(6): 1016–1019.
- Hamwi GJ. Therapy: changing dietary concepts. In: Danowski TS, ed. Diabetes Mellitus: Diagnosis and Treatment. American Diabetes Association, 1964: 73–78.
- Pai MP, Paloucek FP. The origin of the 'ideal' body weight equations. Annals of Pharmacotherapy 2000; 34(9): 1066–1069.
- World Health Organization. Obesity: preventing and managing the global epidemic. WHO Technical Report Series 894 (2000) — BMI classification.
- NHS. Body mass index (BMI) — healthy weight assessment. nhs.uk.