Ideal Body Weight for Dosing

Enter your sex, height, and actual body weight to calculate your Ideal Body Weight (IBW) and Adjusted Body Weight (AdjBW) for medication dosing. The tool returns your IBW, AdjBW, and the recommended dosing weight based on clinical guidelines — useful for dosing weight-based medications like aminoglycosides, vancomycin, and chemotherapy agents.

Disclaimer: This tool is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making any health-related decisions.

Sex *

ft
in
kg

Enter the patient's actual measured body weight in kilograms.

Results

Recommended Dosing Weight

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Ideal Body Weight (IBW)

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Adjusted Body Weight (AdjBW)

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BMI

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Dosing Recommendation

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% Over IBW

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Frequently Asked Questions

What formula is used to calculate Ideal Body Weight (IBW)?

This calculator uses the Devine formula, the most widely accepted clinical standard. For males: IBW = 50 kg + 2.3 kg per inch over 5 feet. For females: IBW = 45.5 kg + 2.3 kg per inch over 5 feet. This formula was originally developed for pharmacokinetic drug dosing.

When should Adjusted Body Weight (AdjBW) be used instead of IBW?

AdjBW is used when a patient is obese — generally defined as actual body weight more than 20–30% above IBW. In these cases, using actual body weight may overdose the patient, while IBW alone may underdose. AdjBW accounts for the fact that adipose tissue does have some drug distribution capacity. AdjBW = IBW + 0.4 × (Actual BW − IBW).

Which medications commonly require weight-based dosing with IBW or AdjBW?

Aminoglycosides (gentamicin, tobramycin, amikacin), vancomycin, heparin infusions, low molecular weight heparins, and many chemotherapy agents are routinely dosed using IBW or AdjBW. Always verify with current institutional protocols or drug references for specific agents.

What is the significance of being more than 30% over IBW?

When a patient's actual body weight exceeds IBW by more than 30% (i.e., they are obese), clinical guidelines generally recommend using Adjusted Body Weight for dosing rather than actual or ideal body weight alone. This threshold is a common clinical cutoff for switching dosing strategies.

Is this calculator appropriate for pediatric patients?

No. The Devine formula and this calculator are intended for adult patients. Pediatric dosing relies on entirely different weight and body surface area-based models. Consult pediatric-specific dosing resources for patients under 18.

What happens if a patient's actual body weight is less than their IBW?

If actual body weight is less than IBW, the patient is underweight, and the actual body weight should be used for dosing rather than IBW. This calculator will flag that situation and recommend actual body weight as the dosing weight.

How is BMI calculated and how does it relate to dosing weight selection?

BMI is calculated as weight (kg) divided by height squared (m²). While BMI provides a general obesity classification, clinical dosing weight decisions are specifically based on the percentage over IBW rather than BMI category alone. Both metrics are shown here for reference.

Can this tool replace clinical judgment or a pharmacist's recommendation?

No. This calculator is intended as a clinical decision support aid only. Drug dosing decisions should always be made in consultation with a licensed pharmacist or physician, taking into account renal function, indication, patient-specific factors, and institutional guidelines.