Adjusted Body Weight Calculator
Calculate Ideal Body Weight (IBW) and Adjusted Body Weight (AdjBW) for drug dosing in obese patients.
Did this tool work for you?
How to use this calculator
The Devine formula calculates IBW from height. AdjBW is used for dosing obese patients because many drugs distribute partly into adipose tissue. It is only applied when actual weight exceeds 130% of IBW.
- 1
Select the patient's sex.
- 2
Enter height in centimetres and actual body weight in kilograms.
- 3
Review the calculated IBW and Adjusted Body Weight.
- 4
Use AdjBW for dosing when actual weight exceeds 130% of IBW.
Frequently asked questions
What is Ideal Body Weight used for?
IBW is used as a reference to determine tidal volume in mechanical ventilation (6 mL/kg IBW for lung-protective ventilation) and as a baseline for calculating AdjBW for drug dosing.
Why not just use actual weight for dosing in obese patients?
Many drugs do not fully distribute into adipose tissue. Using actual weight in obese patients would lead to overdosing. AdjBW provides a weight between IBW and actual weight that better approximates the drug's distribution volume.
When is AdjBW applicable?
AdjBW is used when actual weight exceeds 130% of IBW (i.e., the patient is more than 30% above ideal weight). Below this threshold, actual body weight is typically used.
Does the 0.4 correction factor apply to all drugs?
No. The 0.4 factor is a general estimate. Some drugs (e.g., aminoglycosides) use AdjBW with a 0.4 factor; others use different fractions or lean body mass. Always consult drug-specific dosing references.
Adjusted Body Weight Calculator for Drug Dosing
Why Dosing Weight Matters in Obese Patients
Medication dosing based on actual body weight in obese patients can lead to significant toxicity. Most medications do not distribute fully into fat tissue, so dosing to actual weight overestimates the volume of distribution and results in supratherapeutic drug levels. Adjusted Body Weight corrects for this by interpolating between ideal and actual weight, accounting for the partial drug uptake into adipose tissue.
Common Clinical Applications of IBW and AdjBW
IBW is the foundation for lung-protective mechanical ventilation settings and determines tidal volume targets in ARDS. AdjBW is used for dosing aminoglycosides (gentamicin, tobramycin), vancomycin loading doses, heparin, enoxaparin, and many chemotherapy agents. Always verify against the specific drug's pharmacokinetic data and your institution's dosing protocols.
Learn more from an authoritative source:
CDCMedication Dosage Calculator
Calculate weight-based medication dosage (mg/kg). For educational reference only — always follow prescriber instructions.
IV Drip Rate Calculator
Calculate IV drip rate in mL/hr and drops/min for nursing and clinical reference.
eGFR Calculator (Kidney Function)
Estimate glomerular filtration rate (eGFR) using the CKD-EPI formula to assess kidney function.
Body Surface Area Calculator
Calculate body surface area (BSA) using Mosteller, DuBois, and Haycock formulas. Used for drug dosing and clinical assessment.
Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →