Ideal Body Weight (IBW) & Adjusted BW
Devine formula for IBW, plus adjusted body weight for obese patients
Calculator
Why use it
Lung-protective ventilation (tidal volume 6-8 mL/kg IBW). Drug dosing in obesity (aminoglycosides, vancomycin, heparin). Nutritional assessment baseline.
About
Calculates Ideal Body Weight (IBW) using the Devine formula and Adjusted Body Weight (AdjBW) for obese patients. IBW is used for lung-protective tidal volume calculation (6-8 mL/kg IBW), many medication dosing adjustments, and nutritional calculations. AdjBW (IBW + 0.4 × excess weight) is used for certain drug dosing in obese patients.
When to use
- Setting ventilator tidal volumes (ARDS, all mechanical ventilation)
- Drug dosing adjustments for obesity
- Nutritional assessment
- BMI interpretation context
Formula
Pearls & pitfalls
- Lung-protective TV is ALWAYS based on IBW, not actual weight.
- IBW formula is height-based — does not account for body composition.
- AdjBW = IBW + 0.4 × (Actual Weight - IBW) — used for some drug dosing in obesity.
- Vancomycin and aminoglycosides: use actual body weight (AdjBW or TBW depending on drug).
- For patients shorter than 5 feet (152.4 cm): the formula may give very low values — use clinical judgment.
- Some references use 0.25 instead of 0.4 for the AdjBW correction factor — check specific drug guidelines.
Next steps
For ventilator: TV = 6-8 mL/kg IBW. For drug dosing: check specific drug guidelines (IBW vs. ABW vs. AdjBW). For nutrition: use actual weight for caloric needs but IBW or AdjBW for protein calculations in some guidelines.
Evidence
Devine formula (1974) originally for drug dosing. Adopted for ventilator management after ARDSNet trial (NEJM 2000). IBW-based tidal volumes (6 mL/kg IBW) reduced mortality by 22% in ARDS.