Four formulas, four answers
There is no single agreed definition of ideal body weight. Four formulas are in common clinical use, all built on the same structure — a base weight at five feet, plus a fixed increment per additional inch — but each was derived from a different population for a different purpose.
| Formula | Men | Women |
|---|---|---|
| Devine (1974) | 50.0 + 2.3 per inch over 5 ft | 45.5 + 2.3 per inch over 5 ft |
| Robinson (1983) | 52.0 + 1.9 per inch over 5 ft | 49.0 + 1.7 per inch over 5 ft |
| Miller (1983) | 56.2 + 1.41 per inch over 5 ft | 53.1 + 1.36 per inch over 5 ft |
| Hamwi (1964) | 48.0 + 2.7 per inch over 5 ft | 45.5 + 2.2 per inch over 5 ft |
Why they differ
The Devine formula was never intended as a health target at all — B.J. Devine devised it in 1974 to calculate drug dosages, and it remains the standard for that purpose. It became a general-purpose "ideal weight" formula largely by accident.
Robinson and Miller were both published in 1983 as modifications, fitted to observed data rather than dosing convenience. Hamwi, from 1964, was developed for estimating nutritional needs in people with diabetes and tends to give the highest figures for tall people because of its steep 2.7 kg per inch increment.
Note the structural weakness they all share: below five feet, the increment works in reverse, and none of them was validated for very short or very tall people.
A worked example
The four span nearly 5 kg. The healthy BMI range for this height is far wider — 58.6 kg to 78.9 kg.
Why a range beats a single number
Every formula above returns one figure, which is the wrong shape of answer. Two people of the same height and sex can both be healthy at weights 15 kg apart, depending on muscle mass, bone density and frame size.
The healthy BMI range — 18.5 to 24.9 — is a more honest target, and it is deliberately a range. For someone 178 cm tall that spans 58.6 kg to 78.9 kg. The ideal weight formulas all land comfortably inside it, which tells you the formulas are reasonable but unnecessarily precise.
What matters more than weight
- Body fat percentage — distinguishes muscle from fat, which weight cannot. Use the body fat calculator.
- Waist circumference — abdominal fat carries the most metabolic risk. Keep it under half your height.
- Fitness and strength — cardiorespiratory fitness predicts mortality better than weight in several large cohort studies.
- Blood markers — blood pressure, lipids and fasting glucose describe metabolic health directly.
For calorie targets to move toward a goal weight, see the calorie calculator.
Frequently asked questions
Which ideal weight formula is most accurate?
None is definitively best. Robinson and Miller were fitted to observed population data and are generally preferred for health purposes; Devine remains the clinical standard for drug dosing, which is what it was built for.
Take the range across all four as your target band rather than any single figure.
Does ideal weight depend on age?
The formulas do not use age, but the evidence suggests it should. Older adults appear to have better outcomes at a slightly higher weight — a BMI around 23 to 27 rather than 18.5 to 24.9 — because some reserve helps with recovery from illness.
For children and adolescents these formulas do not apply at all; paediatric growth charts are used instead.
How does body frame affect ideal weight?
Larger frames carry more bone and connective tissue, supporting roughly 10% more weight at the same height. Small frames sit about 10% below.
Use the wrist test: thumb and middle finger around the opposite wrist. Overlapping means small, touching means medium, not meeting means large.
Should athletes use ideal weight formulas?
No. These formulas cannot distinguish muscle from fat, so a muscular athlete will appear overweight by every one of them.
Body fat percentage is the right measure. A 90 kg athlete at 10% body fat is far healthier than a 73 kg sedentary person at 28%.