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)
Always confirm the prescribed dose, frequency, and maximum daily dose against the BNF.
Step-by-step method
- 1
Confirm the prescribed dose per kg
Read the dose in mg/kg or mcg/kg from the prescription, BNF, or local protocol.
- 2
Record the patient’s weight
Use the most recent recorded weight in kilograms. For obese patients, check whether ideal, adjusted, or actual body weight is required.
- 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 BNF maximum 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 once daily for an 80 kg adult.
Answer: 80 × 5 = 400 mg once daily (verify against renal function and trough levels).
Practice calculations for the CRA
500+ exam-style calculation questions with detailed explanations, mapped to the GPhC Common Registration Assessment Part 1.