What these formulas actually do
Each ideal body weight formula sets a base weight at a height of 5 feet and adds a fixed amount of weight for every inch above that. They differ only in the base value and the per-inch increment. Notably, none of them uses your current weight, body-fat percentage or frame size — they are functions of height and sex alone.
It is worth knowing that these formulas were developed for clinical purposes such as estimating drug dosages, not as aesthetic or fitness goals. That origin is why they produce a single reference figure rather than a healthy range.
Four formulas, one 180 cm man
For a man 180 cm tall — about 10.9 inches over 5 feet — here is what each formula produces. The differences come entirely from the different base weights and per-inch increments each author chose.
| Formula | Estimate (180 cm man) | Per inch over 5 ft |
|---|---|---|
| Hamwi (1964) | 77.3 kg | +2.7 kg |
| Devine (1974) | 75.0 kg | +2.3 kg |
| Robinson (1983) | 72.6 kg | +1.9 kg |
| Miller (1983) | 71.5 kg | +1.41 kg |
Why they disagree — and which to trust
The nearly 6 kg spread comes from the different increments: Hamwi adds the most weight per inch of height and Miller the least, so the gap widens for taller people. The later formulas (Robinson and Miller, both 1983) were refinements intended to better fit observed data, and tend to give lower figures than the older Hamwi and Devine equations.
No single formula is authoritatively 'correct,' because ideal weight depends on body composition the formulas cannot see. A more useful reading is the range they collectively produce — here roughly 71–77 kg — combined with a healthy-BMI range and, ideally, a body-composition measure such as body-fat percentage or waist circumference.
Better questions than 'ideal weight'
Because these formulas ignore muscle, frame and fat distribution, they are a starting reference rather than a target. A muscular athlete can sit well above their 'ideal' weight while being lean and healthy. Pairing an IBW range with BMI and a direct body-composition or waist measurement gives a far more meaningful picture than any single ideal-weight number.
Perguntas frequentes
What is the ideal weight for a 180 cm man?
It depends on the formula: estimates range from 71.5 kg (Miller) to 77.3 kg (Hamwi), roughly a 71–77 kg reference range for the same height.
Why do ideal weight calculators give different answers?
They use different formulas (Hamwi, Devine, Robinson, Miller) with different base weights and per-inch increments. None uses body composition, so results diverge.
Were these formulas designed as health goals?
No. They were originally created for clinical purposes such as medication dosing, which is why each gives a single figure rather than a healthy weight range.
Should I aim for my 'ideal body weight'?
Treat it as a rough reference, not a target. It ignores muscle and body composition, so pair it with BMI and a body-fat or waist measurement for a fuller picture.
Referências
- Devine BJ. Gentamicin therapy. Drug Intelligence & Clinical Pharmacy. 1974;8:650-655 (origin of the Devine formula).
- Robinson JD, et al. Determination of ideal body weight for drug dosage calculations. Am J Hosp Pharm. 1983;40(6):1016-1019.
- Hamwi GJ. Therapy: changing dietary concepts. In: Diabetes Mellitus: Diagnosis and Treatment. American Diabetes Association; 1964.