Common Registration Assessment, Part 1
Stones, pounds, inches and metric conversions
Convert body weight and height from imperial to metric using supplied factors, with three original worked questions.
Published 9 October 2026. Independent revision material, not GPhC questions, not for patient care.
Patients sometimes give weight in stones and pounds or height in feet and inches, while dosing uses kilograms and centimetres. The exam gives conversion factors in the question, so the task is to apply them in the right order.
The factors below are stated in each question and are for practice. Always use the figure the question provides rather than one you remember.
The method
- Convert stones to pounds first: multiply by the number of pounds in a stone, then add loose pounds.
- Divide pounds by the pounds-per-kilogram factor given.
- For height, change feet to inches, add inches, then multiply by centimetres per inch.
- Round only at the end to the level asked.
- Check that the result is plausible for an adult.
Three practice questions
Work each one on paper first, then open the answer. All drugs and patients are fictional.
Question 1
Use 1 stone = 14 lb and 1 kg = 2.2 lb. Convert 11 stone 4 lb to kg, to 1 decimal place.
Show the answer
Answer: 71.8 kg
Working: 11 × 14 + 4 = 158 lb. 158 ÷ 2.2 = 71.8 kg.
Question 2
Use 1 inch = 2.54 cm. Convert 5 ft 7 in to cm, to 1 decimal place.
Show the answer
Answer: 170.2 cm
Working: 5 × 12 + 7 = 67 in. 67 × 2.54 = 170.18, so 170.2 cm.
Question 3
Use 1 kg = 2.2 lb. A fictional patient weighs 154 lb and the dose is 2 mg/kg. What is the dose?
Show the answer
Answer: 140 mg
Working: 154 ÷ 2.2 = 70 kg. 2 × 70 = 140 mg.
Plausibility
An adult weight of 7 or 700 kg should look wrong at a glance. A quick estimate catches a divide-or-multiply slip.
Where marks are lost
- Adding stones to pounds without converting stones first.
- Multiplying instead of dividing by 2.2.
- Rounding the weight before applying the dose.
Frequently asked questions
Should I memorise the factors?
Use the factors in the question. They may be rounded for the exam.
When should I round?
At the end. Keep the unrounded weight for any follow-on step.
Sources
- The Pharmaceutical Journal, medication maths: using provided formula
- The Pharmaceutical Journal, preparing for the GPhC pharmaceutical calculations assessment
- 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
- 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
See also the formula sheet, the eight sample questions and the approved calculator page.