Dosage Calculation Practice Questions
Random mg/kg problems with instant checking – single doses, daily totals, lb-to-kg conversion and safe-range checks – plus ten worked examples.
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Worked practice problems
Problem 1. A child weighs 18 kg. Order: 15 mg/kg/dose every 8 hours. Find the single dose and the daily total.
Answer and steps
Single: 18 × 15 = 270 mg. Daily: 270 × 3 = 810 mg.
Problem 2. A child weighs 66 lb. Order: 12 mg/kg/dose. (Use 2.2 lb = 1 kg.)
Answer and steps
66 ÷ 2.2 = 30 kg. 30 × 12 = 360 mg per dose.
Problem 3. A 12 kg toddler is ordered 40 mg/kg/day divided every 6 hours.
Answer and steps
Daily: 12 × 40 = 480 mg. Every 6 h = 4 doses. 480 ÷ 4 = 120 mg per dose.
Problem 4. An infant weighs 8.2 kg. Order: 25 mg/kg/day divided every 12 hours.
Answer and steps
Daily: 8.2 × 25 = 205 mg. 205 ÷ 2 = 102.5 mg per dose.
Problem 5. An adult weighs 154 lb. Order: 5 mg/kg/dose. (Use 2.2 lb = 1 kg.)
Answer and steps
154 ÷ 2.2 = 70 kg. 70 × 5 = 350 mg.
Problem 6. A neonate weighs 4.5 kg. Order: 7.5 mg/kg/dose every 12 hours.
Answer and steps
4.5 × 7.5 = 33.8 mg per dose (33.75 rounded to one decimal).
Problem 7. A 16 kg child is prescribed 150 mg every 8 hours. The reference range is 20-30 mg/kg/day. Is the order within range?
Answer and steps
Prescribed daily: 150 × 3 = 450 mg. Range: 16 × 20 = 320 mg to 16 × 30 = 480 mg. 450 is between 320 and 480 → within the recommended range.
Problem 8. A 25 kg child is prescribed 500 mg every 6 hours. The reference maximum is 60 mg/kg/day. Safe?
Answer and steps
Prescribed daily: 500 × 4 = 2000 mg. Maximum: 25 × 60 = 1500 mg. 2000 > 1500 → above the maximum – verify the order with the prescriber/pharmacist.
Problem 9. A patient weighs 99 lb. Order: 2 mg/kg/dose. (Use 2.2 lb = 1 kg.)
Answer and steps
99 ÷ 2.2 = 45 kg. 45 × 2 = 90 mg.
Problem 10. A 3.6 kg neonate is ordered 50 mg/kg/day divided every 8 hours.
Answer and steps
Daily: 3.6 × 50 = 180 mg. 180 ÷ 3 = 60 mg per dose.
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Educational practice only – values are invented for training and are not clinical recommendations. Reviewed 2026-08-23.