Ideal Body Weight (IBW) Calculator
Calculate your Ideal Body Weight (IBW) using the three most widely cited clinical formulas: Robinson (1983), Devine (1974), and Miller (1983). Enter height in centimetres and select sex for instant results in kilograms. Used in medication dosing, anaesthesia, and nutrition planning.
Key Capabilities
Three validated clinical formulas compared
Calculates IBW using Robinson (1983), Devine (1974), and Miller (1983) formulas simultaneously — letting clinicians see the range across formulas and choose the most appropriate one for their clinical context.
Results in kilograms and pounds simultaneously
IBW outputs display in both kg and lbs at once — useful when switching between metric drug references used in India and the UK versus imperial prescribing guidelines used in the US.
Sex-specific formula constants applied correctly
All three IBW formulas use different baseline constants for male and female patients — a sex selector ensures the correct formula variant is applied for each individual.
How to Use
Select biological sex
Choose male or female. The baseline constant differs by sex in all three IBW formulas — selecting the wrong sex produces clinically incorrect results.
Enter height in centimetres
Input the patient's standing height. For patients who cannot stand, estimated height derived from arm span or knee height measurements may be used.
Compare the three formula outputs
Robinson, Devine, and Miller IBW results appear side by side in kg and lbs. The Devine formula is most commonly cited in drug dosing references; use it when consistency with reference materials matters.
Common Use Cases
- Anaesthetists calculating induction drug dosesAn anaesthetist preparing for surgery on an obese patient calculates IBW to dose propofol correctly — propofol distributes into lean tissue, so dosing to actual body weight risks overdose in high-adiposity patients.
- ICU nurses setting lung-protective tidal volumesA critical care nurse setting up mechanical ventilation uses IBW-based tidal volume targets (6–8 mL/kg IBW) to achieve lung-protective ventilation regardless of the patient's actual body weight.
- Pharmacists dose-adjusting aminoglycosidesA clinical pharmacist calculating gentamicin or tobramycin dosing for an obese patient uses IBW as the weight denominator — aminoglycosides distribute into lean tissue and should not be dosed to total body weight.
Frequently Asked Questions
What is Ideal Body Weight used for in medicine?
IBW is used clinically for weight-based drug dosing (especially antibiotics and anaesthetic agents), ventilator tidal volume calculations, and nutritional assessments. Drugs with poor fat solubility are dosed to IBW rather than actual body weight to avoid toxic accumulation.
Which IBW formula is most commonly used?
The Devine formula (1974) is the most widely cited in clinical practice, particularly for drug dosing and ventilator management. The Robinson formula (1983) is considered slightly more accurate for general population estimates. All three formulas are included so you can compare results.
How is IBW different from BMI healthy weight?
BMI healthy weight gives a range (18.5–24.9) depending on individual height. IBW formulas give a single target weight based solely on height and sex, originally derived from life insurance actuarial data. Neither is a definitive optimal weight — actual healthy weight varies by frame size and muscle mass.
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