Adjusted Body Weight Calculator — Drug Dosing for Obese Patients
Estimate the adjusted body weight (AdjBW) used for drug dosing in obese patients — applies the Devine ideal body weight and adds 40% of excess weight to account for the partial distribution of drugs into adipose tissue.
Sex
cm
kg
Dosing weight for obese patients: IBW + 0.4 × (ABW − IBW)
- 1
Height in inches
175 ÷ 2.54 = 68.9 - 2
Inches over 5 ft (60 in)
68.9 − 60 = 8.9 - 3
Ideal body weight (IBW)
50 + 2.3 × 8.9 = 70.5Devine formula: 50 kg base, +2.3 kg per inch above 5 ft. - 4
0.4 × excess weight
0.4 × (100 − 70.5) = 11.81 - 5
Adjusted body weight
70.5 + 11.81 = 82.3
How does this calculator work?
Adjusted body weight (AdjBW) = IBW + 0.4 × (Actual Weight − IBW), where IBW uses the Devine formula (50 kg for males or 45.5 kg for females at 5 ft, + 2.3 kg per extra inch). AdjBW is used for drug dosing in obese patients when actual weight exceeds IBW — always verify which weight to use against the drug's specific guidance.
Formula
How this is calculated
When dosing medications that distribute partially into adipose (fat) tissue — such as aminoglycosides, vancomycin, and many chemotherapy agents — using actual body weight in obese patients can result in toxic doses, while using ideal body weight alone can result in sub-therapeutic concentrations. Adjusted body weight provides a compromise.
Ideal body weight (IBW) is calculated using the Devine formula (1974): 50 kg for males or 45.5 kg for females at exactly 5 feet (60 inches), plus 2.3 kg for every additional inch of height. Adjusted body weight then adds 40% of the excess weight above IBW: AdjBW = IBW + 0.4 × (ABW − IBW). The 0.4 correction factor reflects the empirical observation that approximately 40% of the excess adipose tissue participates in drug distribution for commonly dosed agents.
AdjBW is only applied when actual body weight exceeds IBW (i.e., the patient is obese). At or below IBW, actual body weight is used for dosing. The specific weight to use — IBW, AdjBW, or ABW — varies by drug and guideline, so always consult the drug's prescribing information and your institution's pharmacy protocols.
Frequently asked questions
Obese patients have proportionally less lean tissue per kilogram of total weight, and many drugs distribute primarily into lean tissue. Using actual weight in obese patients can lead to over-dosing and toxicity. AdjBW corrects for this by using a weight that reflects lean mass plus a partial contribution from excess adipose tissue.
Commonly cited examples include aminoglycoside antibiotics (gentamicin, tobramycin), vancomycin, heparin, and some chemotherapy agents. Always verify with the drug's package insert or your pharmacy team — some drugs use IBW, some use ABW, and some use AdjBW depending on their pharmacokinetics.
The Devine formula (1974) was originally developed to standardise medication dosing and has remained in wide clinical use. It uses height and sex only, ignoring frame size, muscle mass, and age. It tends to underestimate ideal weight in very tall individuals and overestimate it in short individuals. More recent formulas exist but Devine remains the clinical standard for AdjBW calculations.
Also known as
TG we-Calculate Editorial Team. (2026). Adjusted Body Weight Calculator — Drug Dosing for Obese Patients [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/adjusted-weight-calculator
TG we-Calculate Editorial Team. "Adjusted Body Weight Calculator — Drug Dosing for Obese Patients." TG we-Calculate. 2026. https://we-calculate.com/calculator/adjusted-weight-calculator.
TG we-Calculate Editorial Team, "Adjusted Body Weight Calculator — Drug Dosing for Obese Patients," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/adjusted-weight-calculator
@misc{wecalculate_adjusted_weight_calculator, title = {Adjusted Body Weight Calculator — Drug Dosing for Obese Patients}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/adjusted-weight-calculator}}, year = {2026}, note = {TG we-Calculate} }
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