Ideal Body Weight Calculator
Calculate ideal body weight using the Devine, Robinson, Miller, and Hamwi formulas plus adjusted body weight for medication dosing.
MEDICAL DISCLAIMER
This calculator is for educational and clinical reference purposes only. Ideal body weight formulas were originally developed for drug dosing, ventilator settings, and nutritional assessments, not as standalone health indicators. Results must be interpreted by a qualified healthcare professional in the context of the patient's overall clinical picture. Do not use IBW alone to assess health status.
What This Calculator Does
This ideal body weight (IBW) calculator computes IBW using four established formulas: Devine (1974), Robinson (1983), Miller (1983), and Hamwi (1964). Each formula uses the patient height and biological sex to estimate an ideal weight. It also calculates adjusted body weight (AdjBW) for obese patients, which is commonly used in clinical settings for drug dosing, ventilator tidal volume calculations, and nutritional assessments.
The Formula
All four IBW formulas use height in inches above 60 inches (5 feet) as the primary variable. The Devine formula is the most widely used in clinical practice. For patients who exceed their IBW by more than 30%, adjusted body weight uses a correction factor of 0.4 to calculate a dosing weight between IBW and actual weight. Results are displayed in both kilograms and pounds.
Step-by-Step Example
Enter patient data
Male patient, 70 inches (5 foot 10), actual weight 220 lbs (99.8 kg).
Calculate IBW with each formula
Devine: 50 + 2.3 x 10 = 73 kg. Robinson: 52 + 1.9 x 10 = 71 kg. Miller: 56.2 + 1.41 x 10 = 70.3 kg. Hamwi: 48 + 2.7 x 10 = 75 kg.
Calculate adjusted body weight
AdjBW = 73 + 0.4 x (99.8 - 73) = 73 + 10.7 = 83.7 kg.
Apply clinically
Use Devine IBW (73 kg) for ventilator settings. Use AdjBW (83.7 kg) for aminoglycoside dosing in this obese patient.
Real-World Use Cases
Drug Dosing
Many medications (aminoglycosides, certain anesthetics, anticoagulants) require dosing based on IBW or adjusted body weight rather than actual weight to avoid toxicity.
Ventilator Settings
Lung-protective ventilation uses IBW to calculate tidal volumes (typically 6 to 8 mL/kg IBW). Using actual weight in obese patients leads to dangerously high tidal volumes.
Nutritional Assessment
Dietitians use IBW to calculate caloric and protein needs, assess percentage of IBW, and set nutritional goals for patients.
Common Mistakes to Avoid
Using IBW for patients shorter than 5 feet (60 inches). The formulas were not validated for this population and produce inaccurate results below this height.
Using actual body weight when IBW or adjusted body weight is required. This is especially dangerous for ventilator tidal volume calculations and aminoglycoside dosing in obese patients.
Treating IBW as a health target or ideal weight for the patient. These formulas were designed for clinical calculations, not as personal health goals.
Forgetting that different formulas produce different results. The Devine formula is the standard for most clinical applications. Specify which formula you are using in clinical documentation.
Frequently Asked Questions
Accuracy and Disclaimer
MEDICAL DISCLAIMER: This calculator is for educational and clinical reference purposes only. Ideal body weight formulas have known limitations and were developed from specific populations. Results must be interpreted by a qualified healthcare professional in the context of the patient overall clinical picture. Do not use IBW formulas as standalone health assessments. Always consult current clinical guidelines for the specific application (drug dosing, ventilator management, nutritional assessment) and consider patient-specific factors.
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