Common Registration Assessment, Part 1
Alcohol unit calculations for the GPhC assessment
Three original questions on units of alcohol from strength and volume, with the working shown.
Published 13 October 2026. Independent revision material, not GPhC questions, not for patient care.
A unit of alcohol is a fixed amount of pure alcohol: 10 mL, or 8 g. Drinks come in different strengths and sizes, so the number of units has to be worked out from the label.
The NHS gives a one-line method: strength as a percentage ABV, multiplied by the volume in mL, divided by 1,000. Questions usually add a weekly total to compare with the 14 unit guideline.
The method
- Write the formula: units = ABV (%) × volume (mL) ÷ 1,000.
- Check the volume is in mL and the strength is the ABV percentage from the label.
- Multiply strength by volume, then divide by 1,000.
- For several drinks, work out each drink and then add the units.
- Compare any weekly total with the 14 units a week guidance, and keep the working unrounded until the end.
Three practice questions
Work each one on paper first, then open the answer. All patients and prescriptions are fictional.
Question 1
A 175 mL glass of wine is 12% ABV. How many units does it contain?
Show the answer
Answer: 2.1 units
Working: 12 × 175 = 2,100. 2,100 ÷ 1,000 = 2.1 units.
Question 2
A patient drinks 3 pints (568 mL each) of lager at 4% ABV. How many units is that, and how many mL of pure alcohol, given that 1 unit is 10 mL?
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Answer: 6.8 units, which is about 68 mL of pure alcohol
Working: One pint: 4 × 568 ÷ 1,000 = 2.272 units. Three pints: 2.272 × 3 = 6.816, so 6.8 units. Pure alcohol: 6.816 × 10 mL = 68.2 mL.
Question 3
In a week a patient drinks four 250 mL glasses of wine at 13% ABV and two pints (568 mL) of cider at 5% ABV. What is the weekly total in units, and how far is it above 14 units?
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Answer: 18.7 units, which is 4.7 units above 14
Working: Wine: 13 × 250 ÷ 1,000 = 3.25 units, and 3.25 × 4 = 13.0 units. Cider: 5 × 568 ÷ 1,000 = 2.84 units, and 2.84 × 2 = 5.68 units. Total 13.0 + 5.68 = 18.68, so 18.7 units. 18.7 - 14 = 4.7 units above.
Exam approach
Write the formula first, then check that the volume is in mL. A weekly total is just each drink worked out on its own and then added up.
Where marks are lost
- Dividing by 100 instead of 1,000.
- Using litres for the volume while still dividing by 1,000.
- Rounding each drink early and carrying the error into a weekly total.
- Forgetting to multiply by the number of drinks.
Frequently asked questions
What is one unit of alcohol?
The NHS defines one unit as 10 mL or 8 g of pure alcohol.
What is the weekly guideline in the NHS advice?
Men and women are advised not to drink more than 14 units a week on a regular basis, and to spread it over 3 or more days if drinking as much as 14 units.
Sources
The questions above are original and use fictional patients and prescriptions. PreRegExamPrep is not affiliated with or endorsed by the General Pharmaceutical Council.
Practise until the method is automatic
Try 15 free questions with worked answers. No sign-up required.
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See also the formula sheet, the eight sample questions and the approved calculator page.