Drug Calculation Practice Questions With Answers: 40 Questions for Nurses (Tablets, Liquids, IV Rates and Weight-Based Doses)

Drug calculations appear in almost every nursing licensing exam, from NMCN and NCLEX to the NMC CBT and Prometric, and they’re a daily part of safe practice. The only way to get fast and accurate is to practise. Here are 40 questions with worked answers, grouped from easy to harder.

The core formulas

• Tablets or liquids: (What you want ÷ What you’ve got) × What it comes in
• IV rate (mL/hour): Volume (mL) ÷ Time (hours)
• Drip rate (drops/min): (Volume in mL × drop factor) ÷ Time in minutes
• Weight-based dose: Dose per kg × Weight in kg

Common conversions: 1 g = 1,000 mg; 1 mg = 1,000 micrograms; 1 L = 1,000 mL. Always convert to the same unit before calculating.

Section 1: Conversions

1. Convert 1.5 g to mg. Answer: 1,500 mg
2. Convert 500 micrograms to mg. Answer: 0.5 mg
3. Convert 0.125 mg to micrograms. Answer: 125 micrograms
4. Convert 2.5 L to mL. Answer: 2,500 mL
5. Convert 750 mL to L. Answer: 0.75 L

Section 2: Tablets and capsules

6. Prescribed: paracetamol 1 g. Available: 500 mg tablets. Answer: 2 tablets (1,000 ÷ 500)
7. Prescribed: amoxicillin 500 mg. Available: 250 mg capsules. Answer: 2 capsules
8. Prescribed: bisoprolol 2.5 mg. Available: 5 mg tablets (scored). Answer: 0.5 tablet
9. Prescribed: prednisolone 40 mg. Available: 5 mg tablets. Answer: 8 tablets
10. Prescribed: levothyroxine 75 micrograms. Available: 25 microgram tablets. Answer: 3 tablets
11. Prescribed: digoxin 0.0625 mg. Available: 62.5 microgram tablets. Answer: 1 tablet (0.0625 mg = 62.5 micrograms)
12. Prescribed: metformin 1.5 g daily in 3 divided doses. Available: 500 mg tablets. How many tablets per dose? Answer: 1 tablet (1,500 ÷ 3 = 500 mg)

Section 3: Liquids and injections

13. Prescribed: amoxicillin 250 mg. Available: 125 mg/5 mL suspension. Answer: 10 mL (250 ÷ 125 × 5)
14. Prescribed: morphine 5 mg. Available: 10 mg/mL injection. Answer: 0.5 mL
15. Prescribed: furosemide 20 mg IV. Available: 10 mg/mL. Answer: 2 mL
16. Prescribed: gentamicin 80 mg. Available: 40 mg/mL. Answer: 2 mL
17. Prescribed: ondansetron 4 mg. Available: 2 mg/mL. Answer: 2 mL
18. Prescribed: heparin 5,000 units SC. Available: 25,000 units/mL. Answer: 0.2 mL
19. Prescribed: ceftriaxone 1 g IV. A vial of 1 g is reconstituted to 10 mL. You need 750 mg. What volume? Answer: 7.5 mL
20. Prescribed: oral lactulose 15 mL twice daily. How much in 7 days? Answer: 210 mL

Section 4: IV infusion rates (mL/hour)

21. 1,000 mL over 12 hours. Answer: 83.3 mL/hour (round per local policy, usually to 83 mL/hour)
22. 500 mL over 4 hours. Answer: 125 mL/hour
23. 100 mL antibiotic over 30 minutes. Answer: 200 mL/hour
24. 250 mL over 2 hours 30 minutes. Answer: 100 mL/hour (250 ÷ 2.5)
25. A patient needs 3 L of fluid in 24 hours. Answer: 125 mL/hour
26. An infusion is running at 125 mL/hour. How long will 1 L last? Answer: 8 hours

Section 5: Drip rates (drops per minute)

Standard giving sets usually deliver 20 drops/mL for clear fluids, 15 drops/mL for blood sets and 60 drops/mL for paediatric (micro-drip) sets. Check your equipment.

27. 1,000 mL over 8 hours, 20 drops/mL. Answer: 42 drops/min (20,000 ÷ 480 = 41.7)
28. 500 mL over 6 hours, 20 drops/mL. Answer: 28 drops/min (10,000 ÷ 360 = 27.8)
29. 1 unit of blood (300 mL) over 3 hours, 15 drops/mL. Answer: 25 drops/min (4,500 ÷ 180)
30. 100 mL over 1 hour with a micro-drip set (60 drops/mL). Answer: 100 drops/min
31. 1,000 mL over 10 hours, 15 drops/mL. Answer: 25 drops/min (15,000 ÷ 600)

Section 6: Weight-based and paediatric doses

32. A child weighing 12 kg needs paracetamol 15 mg/kg. Answer: 180 mg
33. Using Q32, suspension is 120 mg/5 mL. Answer: 7.5 mL
34. A 20 kg child needs ibuprofen 5 mg/kg. Suspension is 100 mg/5 mL. Answer: 100 mg = 5 mL
35. A 70 kg adult needs enoxaparin 1.5 mg/kg. Answer: 105 mg
36. A 15 kg child needs amoxicillin 30 mg/kg/day in 3 divided doses. Dose per administration? Answer: 150 mg (450 ÷ 3)
37. A neonate weighing 3.2 kg needs gentamicin 5 mg/kg. Available: 10 mg/mL paediatric injection. Answer: 16 mg = 1.6 mL

Section 7: Infusions in units or mg per hour

38. Insulin 50 units in 50 mL. The patient needs 6 units/hour. Answer: 6 mL/hour
39. Dopamine 200 mg in 50 mL. Rate is 3 mL/hour. How many mg/hour? Answer: 12 mg/hour (4 mg/mL × 3)
40. A 60 kg patient needs a drug at 5 micrograms/kg/min. Concentration is 800 micrograms/mL. What’s the rate in mL/hour? Answer: 22.5 mL/hour (5 × 60 = 300 micrograms/min; × 60 = 18,000 micrograms/hour; ÷ 800 = 22.5)

Safety checks before you give the dose

• Does the answer make sense? If you’re about to give 20 tablets or 15 mL of an IV push drug, stop and recheck.
• Check units twice. Mixing mg and micrograms causes 1,000-fold errors.
• Use a calculator, but estimate first.
• Get an independent second check for high-risk medicines such as insulin, heparin, opioids, potassium and paediatric doses.
• Never use trailing zeros (write 5 mg, not 5.0 mg) and always use a leading zero (0.5 mg, not .5 mg).

Practise every day

Do five questions a day for two weeks before any exam. Accuracy builds speed, and speed reduces stress. Most importantly, these skills keep your patients safe.

Further reading

• WHO: Medication Without Harm
• ISMP: Error-prone abbreviations