⚖️ Ideal Body Weight Calculator – Devine, Robinson, Miller & Hamwi Formulas
The Ideal Body Weight (IBW) Calculator estimates the reference body weight for an adult based on their height and biological sex. IBW is widely used in clinical settings for medication dosing, nutrition planning, and ventilator tidal volume calculations. This calculator supports four validated formulas — Devine, Robinson, Miller, and Hamwi — and lets you compare them side by side.
Why Ideal Body Weight Matters
Many pharmacokinetic and nutritional calculations depend on a reference body weight rather than actual body weight. Using actual weight in obese patients, for instance, can overestimate drug distribution volumes, while using IBW alone may underestimate caloric needs in underweight patients. IBW provides a standardized baseline that clinical professionals use as a starting point.
Common clinical applications include:
- Aminoglycoside dosing — gentamicin, tobramycin, and amikacin doses are calculated on IBW
- Lung-protective ventilation — tidal volume targets use IBW (or predicted body weight, which is nearly identical)
- Renal clearance estimation — the Cockcroft–Gault equation recommends IBW or adjusted body weight for obese patients
- Nutrition support — protein and calorie targets in critically ill patients often reference IBW
The Four IBW Formulas
All four formulas use height in inches above 60 inches (5 feet) as the primary variable, with a sex-specific base weight and per-inch increment. For heights below 5 ft, the per-inch factor is subtracted rather than added.
| Formula | Male (kg) | Female (kg) | Year |
|---|---|---|---|
| Devine | 50 + 2.3 × (in − 60) | 45.5 + 2.3 × (in − 60) | 1974 |
| Robinson | 52 + 1.9 × (in − 60) | 49 + 1.7 × (in − 60) | 1983 |
| Miller | 56.2 + 1.41 × (in − 60) | 53.1 + 1.36 × (in − 60) | 1983 |
| Hamwi | 48 + 2.7 × (in − 60) | 45.5 + 2.2 × (in − 60) | 1964 |
where in = height in total inches. The per-inch factor applies positively above 60 inches and negatively below 60 inches.
Worked Example
A male patient is 5 ft 10 in (70 inches) tall. Using the Devine formula:
IBW = 50 + 2.3 × (70 − 60) = 50 + 23 = 73.0 kg (160.9 lb)With Robinson: 52 + 1.9 × 10 = 71.0 kg. With Miller: 56.2 + 1.41 × 10 = 70.3 kg. With Hamwi: 48 + 2.7 × 10 = 75.0 kg.
Enabling Comparison Mode shows all four estimates together in a table and a bar chart, so you can see the spread across formulas (~4–5 kg in this example).
Comparing Your Current Weight
Enter your current weight to see the weight difference (in kg and %) relative to each formula's IBW estimate. A positive difference means your current weight is above the estimate; a negative difference means it is below. This comparison is a reference indicator — not a goal or medical target.
Metric and Imperial Support
Height can be entered in centimeters or feet and inches. Current weight can be in kg or lb. All IBW results are displayed in both units simultaneously, so no manual conversion is needed.
Which Formula Should You Use?
There is no single "best" IBW formula — each was derived from a different study population:
- Devine is the most widely cited in clinical pharmacokinetics and is the default for aminoglycoside dosing guidelines.
- Robinson yields slightly lower values and is used in some nutrition and anesthesia protocols.
- Miller gives the highest estimates and is occasionally used as an upper-bound reference.
- Hamwi is one of the oldest formulas and is still taught in traditional dietetics and nursing curricula.
When in doubt, use Comparison Mode to see the full range and discuss with a clinician which formula is most appropriate for the specific use case.
IBW formulas were developed for average-frame adults and are notappropriate for children, pregnant individuals, elderly adults (>70 years), competitive athletes, or patients with limb amputations. They represent a clinical reference range, not a personal weight goal. Always consult a qualified healthcare professional before applying IBW in any clinical or dietary context.