Drug Calculation Questions for the Prometric Nursing Exam 2026: 20 Worked Problems with Answers on Doses, IV Rates, Drops per Minute, Paediatric Doses, Insulin and Heparin

Every Prometric nursing paper includes drug calculations, usually eight to fifteen questions, and they are the cheapest marks on the exam: pure method, no clinical judgement, and the same five formulas every time. They are also where candidates throw marks away by rushing. This article gives the formulas, twenty worked problems in the exam's style, and the traps.

The five formulas

Type	Formula
Tablets or volume	Dose required ÷ dose per tablet (or per mL) = number of tablets (or mL). For liquids: (required ÷ stock strength) × stock volume.
Weight-based dose	Dose per kg × weight in kg = total dose.
Infusion rate (pump)	Total volume in mL ÷ time in hours = mL per hour.
Drip rate (gravity)	(Total volume in mL × drop factor) ÷ time in minutes = drops per minute.
Concentration-based infusion	Work out mg per mL (or mcg per mL) in the bag first, then dose per minute or hour ÷ concentration = mL per hour.

Conversions: 1 g = 1,000 mg; 1 mg = 1,000 mcg; 1 L = 1,000 mL; 1 kg = 2.2 lb; 1% = 1 g per 100 mL (10 mg per mL); 1:1,000 = 1 mg per mL; 1:10,000 = 0.1 mg per mL.

Oral doses

Problem 1

Prescribed: amoxicillin 750 mg. Stock: 250 mg capsules. How many capsules?

Answer: 3 capsules. 750 ÷ 250 = 3.

Problem 2

Prescribed: digoxin 125 micrograms. Stock: 0.25 mg tablets. How many tablets?

Answer: Half a tablet. Convert first: 0.25 mg = 250 mcg; 125 ÷ 250 = 0.5. The trap is mixing units.

Problem 3

Prescribed: paracetamol 360 mg. Stock: suspension 120 mg in 5 mL. Volume?

Answer: 15 mL. (360 ÷ 120) × 5 = 15 mL.

Problem 4

Prescribed: furosemide 30 mg. Stock: oral solution 10 mg per mL. Volume?

Answer: 3 mL. 30 ÷ 10 = 3.

Weight-based doses

Problem 5

A child weighs 18 kg. Prescribed: cefalexin 25 mg/kg/day in two divided doses. Stock: 125 mg in 5 mL. Volume per dose?

Answer: 9 mL per dose. 25 × 18 = 450 mg per day; ÷ 2 = 225 mg per dose; (225 ÷ 125) × 5 = 9 mL.

Problem 6

A patient weighs 154 lb. Prescribed: enoxaparin 1 mg/kg. Dose?

Answer: 70 mg. 154 ÷ 2.2 = 70 kg; 1 × 70 = 70 mg.

Problem 7

A 4 kg neonate is prescribed gentamicin 5 mg/kg. Stock: 20 mg in 2 mL. Volume?

Answer: 2 mL. 5 × 4 = 20 mg; 20 mg is 2 mL of stock. Neonatal doses are double-checked by two nurses.

IV infusion rates

Problem 8

1,000 mL of 0.9% sodium chloride is to run over 8 hours by pump. Rate?

Answer: 125 mL per hour. 1,000 ÷ 8 = 125.

Problem 9

500 mL is to run over 6 hours through a giving set with a drop factor of 20 drops per mL. Drops per minute?

Answer: About 28 drops per minute. (500 × 20) ÷ (6 × 60) = 10,000 ÷ 360 = 27.8.

Problem 10

100 mL of antibiotic is to be infused over 30 minutes using a microdrip set (60 drops per mL). Drops per minute?

Answer: 200 drops per minute. (100 × 60) ÷ 30 = 200. With a microdrip set, drops per minute equals mL per hour, so 200 mL per hour.

Problem 11

An infusion is running at 83 mL per hour from a 1,000 mL bag. How long will it last?

Answer: About 12 hours. 1,000 ÷ 83 = 12.05.

Problem 12

A unit of packed red cells (300 mL) is to run over 3 hours with a blood-giving set of 15 drops per mL. Drops per minute?

Answer: 25 drops per minute. (300 × 15) ÷ 180 = 4,500 ÷ 180 = 25.

Concentration-based infusions

Problem 13

Heparin 25,000 units is in 500 mL of 5% dextrose. The prescription is 1,000 units per hour. Rate?

Answer: 20 mL per hour. 25,000 ÷ 500 = 50 units per mL; 1,000 ÷ 50 = 20 mL per hour.

Problem 14

Insulin 50 units is in 50 mL of 0.9% sodium chloride. The prescription is 4 units per hour. Rate?

Answer: 4 mL per hour. 50 ÷ 50 = 1 unit per mL; 4 units = 4 mL per hour. Only insulin syringes are used to draw up insulin.

Problem 15

Dopamine 400 mg is in 250 mL. A 70 kg patient is prescribed 5 mcg/kg/min. Rate?

Answer: About 13 mL per hour. Concentration: 400 mg = 400,000 mcg ÷ 250 = 1,600 mcg per mL. Dose: 5 × 70 = 350 mcg per minute = 21,000 mcg per hour; 21,000 ÷ 1,600 = 13.1 mL per hour.

Problem 16

Noradrenaline 4 mg is in 50 mL. The infusion is running at 6 mL per hour for a 60 kg patient. Dose in mcg/kg/min?

Answer: About 0.13 mcg/kg/min. 4,000 mcg ÷ 50 = 80 mcg per mL; 6 mL per hour = 480 mcg per hour = 8 mcg per minute; 8 ÷ 60 = 0.133.

Problem 17

Potassium chloride 20 mmol is to be added to 1,000 mL to run over 8 hours. Stock: 20 mmol in 10 mL. Volume to add and rate?

Answer: Add 10 mL; run at 125 mL per hour. Peripheral potassium is limited to about 10 mmol per hour, so 20 mmol over 8 hours (2.5 mmol per hour) is safe.

Percentages, ratios and reconstitution

Problem 18

Adrenaline 1:1,000 is prescribed at 0.5 mg intramuscularly for anaphylaxis. Volume?

Answer: 0.5 mL. 1:1,000 is 1 mg per mL. The 1:10,000 preparation (0.1 mg per mL) is for intravenous use in cardiac arrest.

Problem 19

How many grams of glucose are in 500 mL of 10% dextrose?

Answer: 50 g. 10% is 10 g per 100 mL; × 5 = 50 g.

Problem 20

A vial of ceftriaxone 1 g is reconstituted with 9.6 mL of diluent to give 10 mL. Prescribed: 750 mg. Volume?

Answer: 7.5 mL. 1,000 mg in 10 mL is 100 mg per mL; 750 ÷ 100 = 7.5 mL.

The traps that cost marks

• Units: micrograms written as mcg or µg, milligrams as mg. Convert before you divide.
• Per day versus per dose: a daily dose divided into three is one third per dose.
• Drop factor: 10, 15, 20 or 60 drops per mL. The question always tells you; read it.
• Rounding: round drops per minute to the nearest whole number; mL per hour to one decimal where the pump allows; never round paediatric doses up.
• Weight in pounds: divide by 2.2 before anything else.
• Reasonableness: if the answer is 40 tablets or 2,000 mL per hour, you have made an error. Recheck.

How to practise

Do ten calculations a day for three weeks, timed, until each takes under a minute. The Registered Nurse bank has a pharmacology and calculations chapter with explanations, and the nursing sample questions mix calculations with clinical items as the exam does. Pharmacists and pharmacy technicians have their own calculation sets (pharmacist questions, pharmacy technician questions). The wider study method is in the 30-day study plan.

Frequently asked questions

How many drug calculation questions are in the Prometric nursing exam?

Usually eight to fifteen, mixed into the pharmacology and fundamentals domains.

Can I use a calculator in the Prometric exam?

An on-screen calculator is usually available in the exam software; personal calculators are not allowed. Practise with the basic on-screen type.

Which formula do I need for drops per minute?

Volume in mL multiplied by the drop factor, divided by the time in minutes.

Are calculations the same in the DHA and SCFHS nursing exams?

Yes. The same five formulas apply across every Gulf nursing paper.

Do assistant nurses get calculation questions?

Yes, simpler ones on tablets, oral liquids and basic infusion rates (assistant nurse sample questions).