Common Registration Assessment, Part 1
Drip rate calculations: drops per minute
Three original questions that turn a volume and time into a whole number of drops per minute.
Published 4 October 2026. Independent revision material, not GPhC questions, not for patient care.
A gravity drip is set by counting drops. You need the volume, the time and the drop factor printed on the giving set, which is the number of drops per mL.
Work to mL per hour first, then convert to drops per minute. Drops are counted in whole numbers, so say how you rounded.
The method
- Find mL per hour: volume ÷ hours.
- Multiply by drops per mL.
- Divide by 60 to get drops per minute.
- Round to a whole number as the question asks.
Three practice questions
Work each one on paper first, then open the answer. All drugs and patients are fictional.
Question 1
1,000 mL is to run over 8 hours through a giving set that delivers 20 drops per mL. How many drops per minute?
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Answer: 41.7, so about 42 drops/min
Working: 1,000 ÷ 8 = 125 mL/h. 125 × 20 ÷ 60 = 41.7 drops/min, rounded to 42.
Question 2
500 mL is to run over 6 hours using a 15 drops per mL set. How many drops per minute?
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Answer: about 21 drops/min
Working: 500 ÷ 6 = 83.3 mL/h. 83.3 × 15 ÷ 60 = 20.8, rounded to 21 drops/min.
Question 3
350 mL of blood is to be given over 3 hours using a 15 drops per mL set. What is the drip rate?
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Answer: about 29 drops/min
Working: 350 ÷ 3 = 116.7 mL/h. 116.7 × 15 ÷ 60 = 29.2, rounded to 29 drops/min.
Where drip rates fit
A drip rate is an infusion rate expressed as drops per minute, so the volume and time steps are the same as in the infusion rates page. The drop factor is printed on the giving set and is normally stated in the question. Check the question for any maximum rate it asks you to respect.
Where marks are lost
- Skipping the divide by 60.
- Using the wrong drop factor.
- Giving a decimal where drops must be whole.
Frequently asked questions
What drop factors are common?
15 and 20 drops per mL are common for standard sets. Microdrip sets deliver 60 drops per mL. The question gives the figure you need.
Why divide by 60?
The rate in mL per hour is per 60 minutes, and you want drops per minute.
Sources
- The Pharmaceutical Journal, medication maths: infusion rates (4 April 2025)
- GPhC, Common Registration Assessment specification and permitted items for 2026
The questions above are original and use fictional drugs. PreRegExamPrep is not affiliated with or endorsed by the General Pharmaceutical Council.
Practise until the method is automatic
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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
- Body surface area calculations
- Creatinine clearance (Cockcroft-Gault) calculations
- Moles and millimoles calculations
- Displacement volume calculations for reconstitution
See also the formula sheet, the eight sample questions and the approved calculator page.