Common Registration Assessment, Part 1
Fingertip unit calculations for the GPhC assessment
Three original questions on fingertip units, with the working shown.
Published 14 October 2026. Independent revision material, not GPhC questions, not for patient care.
A fingertip unit is a practical way to measure how much cream or ointment to use. One unit is the amount squeezed from the tube onto the end of an adult finger. DermNet NZ notes that accurate quantities matter most for topical steroids.
The mass in one unit depends on age and sex (DermNet NZ gives about a third of the adult amount at 4 years and about a quarter at 6 months to 1 year; the body-area figures in the table are adult figures, so these questions use adults), and the number of units depends on the body area. Questions usually ask for grams per application, then scale to a day, a week or a course and compare with the tube size.
The method
- Write the number of fingertip units for each body area from the table you are given.
- Add the units for every area treated in one application.
- Multiply by the grams in one unit for that patient, for example 0.5 g for an adult male or 0.4 g for an adult female.
- Multiply by the number of applications a day and the number of days.
- Divide by the tube size and round up to a whole tube if the question asks how many tubes to supply.
Three practice questions
Work each one on paper first, then open the answer. All patients and prescriptions are fictional.
Question 1
An adult woman applies a cream to both legs once daily. One leg takes 6 fingertip units and one unit is 0.4 g. How much cream is used in one day, and in one week?
Show the answer
Answer: 4.8 g a day, 33.6 g a week
Working: Two legs: 2 × 6 = 12 units. 12 × 0.4 g = 4.8 g. Over 7 days: 4.8 × 7 = 33.6 g.
Question 2
An adult man applies a cream twice daily for 14 days to his face and neck (2.5 units) and both hands (1 unit each). One unit is 0.5 g. How much cream is needed, and how many 30 g tubes?
Show the answer
Answer: 63 g, so 3 tubes of 30 g
Working: Units per application: 2.5 + 1 + 1 = 4.5. Grams per application: 4.5 × 0.5 = 2.25 g. Per day: 2.25 × 2 = 4.5 g. Over 14 days: 4.5 × 14 = 63 g. 63 ÷ 30 = 2.1, so 3 tubes.
Question 3
An adult man applies a cream once daily to both feet (2 units each) and both hands (1 unit each). One unit is 0.5 g. How much is used in a day and a week, and how long does a 50 g tube last?
Show the answer
Answer: 3 g a day and 21 g a week, so a 50 g tube lasts about 2.4 weeks
Working: Units: 2 × 2 + 2 × 1 = 6. 6 × 0.5 = 3 g a day. 3 × 7 = 21 g a week. 50 ÷ 21 = 2.4 weeks, which DermNet NZ gives as about 2 and a half weeks.
Exam approach
Count units for each area first, then convert to grams with the right unit mass, then scale to the course.
Where marks are lost
- Using the female unit of 0.4 g for a man (DermNet gives 0.5 g for an adult male), or the male unit of 0.5 g for a woman (0.4 g for an adult female).
- Counting one leg or one arm when both are treated.
- Forgetting to multiply by the number of applications a day.
- Rounding the number of tubes down instead of up.
Frequently asked questions
What is a fingertip unit?
DermNet NZ describes it as the amount of cream squeezed out of its tube onto the end of the finger. It was described by Long and Finlay in 1991 as a convenient way to measure how much cream to prescribe.
How much does one unit hold?
DermNet NZ gives 0.5 g for an adult male and 0.4 g for an adult female. A child aged 4 years has about a third of the adult amount, and an infant of 6 months to 1 year about a quarter.
Sources
- DermNet NZ, fingertip unit
- GPhC, Common Registration Assessment specification and permitted items for 2026
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
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