Dose by Weight Calculator
Calculate weight-based doses (mg/kg or mcg/kg) for any patient. Includes total daily dose and per-dose breakdown.
Calculate the dose based on patient weight and prescribed mg/kg dosing.
Formula
Dose = Weight (kg) × Dose per kg (mg/kg or mcg/kg)
Convert pounds to kilograms (1 lb = 0.4536 kg) before applying. Always confirm against FDA labeling and Lexicomp / Micromedex.
Step-by-step method
- 1
Confirm the prescribed dose per kg
Read the dose in mg/kg or mcg/kg from the prescription, FDA label, or institutional protocol.
- 2
Record the patient's weight
Use the most recent recorded weight in kilograms. For obese patients, decide whether ideal, adjusted, or actual body weight is appropriate (e.g. ideal for aminoglycosides, adjusted for vancomycin if BMI ≥ 30).
- 3
Multiply weight by dose per kg
Total dose = Weight × Dose/kg.
- 4
Check against the maximum daily dose
Compare the calculated dose with the FDA-labeled maximum and your local protocol to ensure it is safe and within the licensed range.
- 5
Round to a sensible strength
Round to a strength that matches available formulations (tablet sizes, vial strengths) where appropriate.
Worked example
Scenario: Prescribe gentamicin 5 mg/kg IV q24h for an 80 kg adult.
Answer: 80 × 5 = 400 mg q24h (verify against renal function and trough levels).
Practice calculations for the NAPLEX
350+ exam-style calculation questions with detailed explanations, mapped to NABP NAPLEX competency Area 4 (Perform Calculations).