Common Registration Assessment, Part 1
Paracetamol syrup calculations for children
Three original questions on converting between syrup volume and milligrams, using the NHS children's paracetamol doses.
Published 13 October 2026. Independent revision material, not GPhC questions, not for patient care.
Children's paracetamol syrup comes in two strengths on the NHS page: infant syrup, 120 mg in 5 mL, for children under 6 years, and six plus syrup, 250 mg in 5 mL, for children aged 6 and over.
The dose is given in mL by age, so the calculation is usually to turn that volume into milligrams, check the daily total, or work out how many doses a bottle holds.
The method
- Find the strength per mL: divide the mg by the mL in the label, for example 120 mg ÷ 5 mL = 24 mg per mL.
- Multiply the volume to give by the mg per mL to get the dose in mg.
- Multiply the dose by the number of doses in 24 hours. The NHS maximum is 4 doses in 24 hours, at least 4 hours apart.
- For a bottle, divide the bottle volume by the volume per dose and round down to whole doses.
- Check the strength and the age band before you pick the volume.
Three practice questions
Work each one on paper first, then open the answer. All patients and prescriptions are fictional.
Question 1
A 2 year old is given 7.5 mL of infant paracetamol syrup, 120 mg in 5 mL. How many mg is that?
Show the answer
Answer: 180 mg
Working: 120 ÷ 5 = 24 mg per mL. 24 × 7.5 = 180 mg.
Question 2
A 4 year old is given 10 mL of infant syrup (120 mg in 5 mL) four times in 24 hours. What is the total in mg and in mL?
Show the answer
Answer: 960 mg, which is 40 mL
Working: Per dose: 24 mg per mL × 10 mL = 240 mg. Four doses: 240 × 4 = 960 mg. Volume: 10 mL × 4 = 40 mL.
Question 3
A 9 year old is given 7.5 mL of six plus syrup, 250 mg in 5 mL. What is the dose in mg, and how many full doses are in a 100 mL bottle?
Show the answer
Answer: 375 mg, and 13 full doses
Working: 250 ÷ 5 = 50 mg per mL. 50 × 7.5 = 375 mg. 100 ÷ 7.5 = 13.3, so 13 full doses.
Exam approach
Write mg per mL beside the label strength before you read the dose. If the age is under 6 use the infant strength, and from 6 use the six plus strength.
Where marks are lost
- Using the 120 mg per 5 mL strength for a six plus syrup question.
- Giving the dose as 5 mL when the label strength changes the mg you need.
- Rounding up the number of doses in a bottle.
- Forgetting that the NHS limit is 4 doses in 24 hours with at least 4 hours between doses.
Frequently asked questions
Can I use a kitchen teaspoon?
No. The NHS page says to use the oral syringe or the measuring spoon that comes with the medicine, not a kitchen teaspoon or any other household spoon, because it will not measure the right amount. If there is no syringe or spoon, ask the pharmacist for one.
Is there a different rule after the MenB vaccinations?
Yes. The NHS page says babies given the MenB vaccine at 8 and 16 weeks can have 3 doses of paracetamol, rather than the usual 2 at that age.
Sources
- NHS, how and when to give paracetamol for children
- 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
Try 15 free questions with worked answers. No sign-up required.
More calculation topics
- Dose by weight calculations for the GPhC assessment
- Volume to give: liquid medicine calculations
- Percentage strength calculations: w/v, w/w and ratios
- Dilution calculations with C1V1 = C2V2
- Infusion rate calculations in mL per hour
- Drip rate calculations: drops per minute
- Body surface area calculations
- Creatinine clearance (Cockcroft-Gault) calculations
- Moles and millimoles calculations
- Displacement volume calculations for reconstitution
- Quantity to supply calculations
- Using a provided formula in calculations
- Dose information from packaging and labels
- Diluting a stock to a lower strength
- Medicine cost and switch calculations
- Rounding rules in calculations
- Enteral feed rate calculations
- Electrolyte content over time
- Infusion dose per kg per hour
- Rounding doses to measurable volumes
- Relative risk and relative risk reduction
- Absolute risk reduction and number needed to treat
- Odds ratio and confidence intervals
- Relative versus absolute risk reduction
- Loading dose and volume of distribution
- Top-up doses from measured drug levels
- Salt correction factors
- Mass and molar drug concentrations
- Half-life and falling drug levels
- Steady-state concentration and infusion rate
- Bioavailability and equivalent oral doses
- Oral maintenance dose and dosing interval
- Elimination rate constant and half-life
- Accumulation towards steady state
- Ratio strengths and one in X
- Serial dilution factors
- Mixing solutions of different strengths
- Tablet quantities for reducing regimens
- Equivalent doses from provided conversion tables
- Thresholds and dose-banding algorithms
- Unit conversions for mass and volume
- Units and units per mL
- Reconstituting powders and final concentration
- Millimoles and milliequivalents
- Infusion time and volume remaining
- Days supply from pack sizes
- Percentage w/v and w/w conversions
- Ideal and adjusted body weight from formulae
- Diluting creams and ointments by weight
- Scaling a formula to a batch size
- Age-band doses from a provided table
- Tablet fractions and split doses
- Stones, pounds, inches and metric conversions
- Micrograms per minute from mg per hour
- Percentage change and mark-up
- Molar solutions and mass per volume
- Osmolarity from component concentrations
- Direct proportion and cross-multiplication
- Scientific notation and very small quantities
- Stock use and reorder quantities
- Parts per million and very dilute solutions
- Sodium chloride equivalents and isotonic solutions
- Density and specific gravity conversions
- Doses per day and hours between doses
- Finding the volume of diluent to add
- Capping a dose at a stated maximum
- Whole vials and ampoules to draw up
- Reading values from a provided graph
- Micrograms per kg per minute infusions
- Percentage composition of a compound preparation
- Suppository displacement values
- Isotonicity by freezing point depression
- Energy content of parenteral nutrition
- Syringe driver rate calculations
- Area under the curve calculations
- Renal dose adjustments using provided bands
- Insulin units and infusion calculations
- Working backwards from a stated dose
- Doses and days from multi-dose devices
- Combined additives in one infusion
- BMI calculations for the GPhC assessment
- Fewest tablets to make a dose
- Clearance from half-life and volume of distribution
- Maintenance fluid requirements by weight
- Sodium load from effervescent tablets
- Ethanol content of liquid preparations
- Oxygen cylinder duration calculations
- Urine output and fluid balance calculations
- Quantities for titration packs
- Infusion line priming and dead space
- Alcohol unit calculations for the GPhC assessment
- Ibuprofen liquid calculations for children
- Vitamin D conversions for the GPhC assessment
- Ferrous sulfate drops and tablet calculations
- Amoxicillin liquid and capsule calculations
- Folic acid dose and quantity calculations
- Adult paracetamol and the daily maximum
- Calcium and iron intake calculations
- Salt limit calculations by age
See also the formula sheet, the eight sample questions and the approved calculator page.