Common Registration Assessment, Part 1
Enteral feed rate calculations
Energy needs, a feed strength and a feeding window. Three original questions on rate and quantity.
Published 5 October 2026. Independent revision material, not GPhC questions, not for patient care.
The Pharmaceutical Journal's rounding guide uses an enteral feeding question to show when to round: a patient on a gastrostomy feed needs a set number of kcal over 24 hours, the product has a kcal per 100 mL strength, and the feed runs for only part of the day.
The method is a chain of unit conversions. Turn the strength into kcal per mL, work out the volume that supplies the energy, then divide by the hours the feed runs.
The method
- Convert the strength to kcal per mL.
- Divide the energy needed by kcal per mL to get the volume.
- Divide the volume by the feeding hours for a rate in mL/hour.
- Round only as the question instructs, and round up for cartons.
Three practice questions
Work each one on paper first, then open the answer. All drugs and patients are fictional.
Question 1
A patient needs 1,550 kcal over 24 hours from an enteral feed that contains 150 kcal per 100 mL. The feed runs for 16 hours overnight. What rate in mL/hour is needed, to the nearest whole number?
Show the answer
Answer: 65 mL/hour
Working: 150 kcal per 100 mL is 1.5 kcal/mL. 1,550 ÷ 1.5 = 1,033.33 mL for the day. Over 16 hours that is 64.58 mL/hour, which rounds to 65. The daily energy is delivered in the hours the feed runs, not across 24.
Question 2
A feed containing 100 kcal per 100 mL runs at 85 mL/hour for 12 hours. How many kcal does the patient receive?
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Answer: 1020 kcal
Working: 85 × 12 = 1,020 mL. At 1 kcal/mL that is 1,020 kcal.
Question 3
A patient needs 2,000 kcal a day. The feed provides 1.2 kcal/mL and comes in 500 mL cartons. How many cartons are needed for 7 days?
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Answer: 24 cartons
Working: 2,000 ÷ 1.2 = 1,666.7 mL a day. × 7 = 11,666.7 mL. ÷ 500 = 23.33 cartons, so 24 cartons: you cannot supply part of a carton.
The journal's feed example
In the guide, a woman needs 1,600 kcal per 24 hours from a feed containing 150 kcal per 100 mL, fed over 14 hours. The working converts the strength to kcal/mL, finds the volume, divides by the hours and rounds to the nearest whole number. The numbers on this page are different.
Where marks are lost
- Dividing by 24 hours when the feed only runs for part of the day.
- Using kcal per 100 mL as if it were kcal per mL.
- Rounding down cartons when the supply must cover the whole period.
Frequently asked questions
Is the feed rate the same as the daily volume divided by 24?
Only if the feed runs all day. If it runs for 14 or 16 hours, divide by those hours.
Do I round the rate?
Follow the question. If it says nearest whole number, round at the end of the rate step.
Sources
- The Pharmaceutical Journal, a guide to rounding for pharmacy students and trainees (27 October 2021)
- 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
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
- Electrolyte content over time
- Infusion dose per kg per hour
- Rounding doses to measurable volumes
See also the formula sheet, the eight sample questions and the approved calculator page.