Common Registration Assessment, Part 1
Micrograms per minute from mg per hour
Practise converting between mg/hour and micrograms/minute and finding a pump rate, with three original worked questions.
Published 9 October 2026. Independent revision material, not GPhC questions, not for patient care.
Infusion orders can be written per hour or per minute, and in different mass units. You need two conversions: 1 mg = 1000 micrograms and 1 hour = 60 minutes.
The numbers are fictional and for arithmetic practice only. Change the mass unit and the time unit separately and write each step on its own line.
The method
- Write the rate with both units, for example mg per hour.
- Convert mass: mg to micrograms multiplies by 1000.
- Convert time: per hour to per minute divides by 60.
- To find a pump rate in mL per hour, divide mg per hour by concentration in mg per mL.
- Check the size of the answer against the starting rate.
Three practice questions
Work each one on paper first, then open the answer. All drugs and patients are fictional.
Question 1
Convert 6 mg/hour to micrograms/minute.
Show the answer
Answer: 100 micrograms/minute
Working: 6 mg = 6000 micrograms. 6000 ÷ 60 = 100 micrograms/minute.
Question 2
A fictional rate is 5 micrograms/kg/minute for a patient weighing 80 kg. Express this in mg/hour.
Show the answer
Answer: 24 mg/hour
Working: 5 × 80 = 400 micrograms/minute. 400 × 60 = 24 000 micrograms/hour = 24 mg/hour.
Question 3
A fictional order is 500 micrograms/minute. The solution is 4 mg/mL. What pump rate in mL/hour is needed?
Show the answer
Answer: 7.5 mL/hour
Working: 500 × 60 = 30 000 micrograms/hour = 30 mg/hour. 30 ÷ 4 = 7.5 mL/hour.
Unit line
Write the unit after every number. If the units on the left and right of an equals sign do not match, an error is hiding.
Where marks are lost
- Dividing by 60 when the rate should be multiplied by 60.
- Forgetting the factor of 1000 between mg and micrograms.
- Using micrograms in the same line as mg per mL.
Frequently asked questions
Do I convert mass or time first?
Either order works. Doing one at a time and writing the unit each time avoids slips.
Why check the size of the answer?
A factor of 1000 or 60 out is the usual error and often gives an unreasonable pump rate.
Sources
- The Pharmaceutical Journal, medication maths: using provided formula
- The Pharmaceutical Journal, medication maths: quantities to supply and using provided formulae
- GPhC, 2026 assessment specification and permitted items
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
- 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
- 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
See also the formula sheet, the eight sample questions and the approved calculator page.