Drug Dosage Calculator
Calculate accurate drug doses using weight-based (mg/kg), BSA-based (mg/m²), or fixed dosing methods. Includes safety range validation, volume to administer, and daily dose summary. For adults and pediatric patients.
💊 Calculate Drug Dose
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How Drug Dosage Calculations Work
Accurate drug dosage calculation is one of the most critical skills in clinical practice. Errors in drug dosing are among the leading causes of preventable adverse events in healthcare. This calculator supports three dosing methods used across all clinical settings.
Weight-Based Dosing (mg/kg)
Weight-based dosing is the standard for most medications, especially in pediatric patients. The prescribed dose in mg/kg is multiplied by the patient's weight to give the single dose. A maximum dose cap is applied where a standard adult ceiling dose exists.
- Formula: Single Dose (mg) = Dose (mg/kg) × Weight (kg)
- If max dose is set: Single Dose = min(calculated dose, max dose)
BSA-Based Dosing (mg/m²)
Body Surface Area dosing is primarily used for chemotherapy and some paediatric drugs. BSA is calculated using the Mosteller formula — the most commonly used method in clinical practice:
- BSA (m²) = √((Height cm × Weight kg) / 3600)
- Single Dose (mg) = Dose (mg/m²) × BSA
Volume to Administer
Once the dose in mg is known, this calculator converts it to the volume to administer based on the available drug concentration. For patients with renal impairment, use our GFR calculator first to assess whether dose reduction is required. For intravenous administration, use the result with our IV drip rate calculator.
Safety Range Checking
Entering a known safe dose range (min and max mg/kg) triggers an automatic safety classification — Safe, Caution, or Outside Range. This is especially important for drugs with narrow therapeutic windows. Always cross-reference with current formulary guidelines and verify with a licensed pharmacist.
⚠️ This tool is for informational and educational purposes only. All drug dosing decisions must be verified by a licensed prescriber or pharmacist. Never administer a drug based solely on a calculator result.