Updated November 13, 2026. Worked examples written by RxReady. For the official blueprint, see pebc.ca.
The types that come up most
| Type | What it asks | Set-up |
|---|---|---|
| Days supply | How long a package lasts | Total doses in package / doses per day |
| Weight-based dosing | Dose for a child or a mg/kg drug | mg/kg x kg, then convert to mL |
| Percent strength | w/v, w/w, v/v | % w/v = g per 100 mL |
| Millimoles and mEq | Electrolytes like KCl | mg / molecular weight = mmol; mEq = mmol x valence |
| Dilutions | Making a weaker strength | C1 x V1 = C2 x V2 |
| Infusion rates | mL/h or drops/min | Dose per hour / concentration; drops = mL x drop factor |
| Creatinine clearance | Renal dose adjustment | Cockcroft-Gault |
Worked example 1: millimoles of potassium
How many millimoles of potassium are in 10 mL of potassium chloride 20% w/v? (Molecular weight of KCl = 74.5 g/mol)
- 20% w/v means 20 g in 100 mL, so 10 mL contains 2 g = 2000 mg.
- 2000 mg / 74.5 mg per mmol = 26.8 mmol of KCl.
- Each KCl gives one K+, so that's 26.8 mmol of potassium.
The trap answers are usually off by a factor of 10 (2.7 or 268). If your answer looks like one of those, recheck the % step.
Worked example 2: pediatric dose to mL
Ibuprofen suspension 100 mg/5 mL, 10 mg/kg per dose, for an 18 kg child. What volume per dose?
- Dose: 10 mg/kg x 18 kg = 180 mg.
- Concentration: 100 mg/5 mL = 20 mg/mL.
- Volume: 180 mg / 20 mg/mL = 9 mL.
Worked example 3: days supply
Salbutamol MDI, 200 actuations per inhaler, 2 puffs four times daily. How many days does one inhaler last?
- Per day: 2 puffs x 4 = 8 actuations.
- 200 / 8 = 25 days.
Worked example 4: dilution
How much 10% solution do you need to make 500 mL of a 2% solution?
- C1 x V1 = C2 x V2, so 10% x V1 = 2% x 500 mL.
- V1 = 1000 / 10 = 100 mL of the 10% solution, made up to 500 mL.
Worked example 5: creatinine clearance
Cockcroft-Gault: CrCl (mL/min) = [(140 - age) x weight (kg) x F] / serum creatinine (µmol/L), where F is about 1.23 for men and 1.04 for women when creatinine is in µmol/L.
A 70-year-old woman, 60 kg, serum creatinine 100 µmol/L: (70 x 60 x 1.04) / 100 = about 44 mL/min.
Five habits that save marks
- Write every unit and cancel them. Most wrong answers are unit errors, not math errors.
- Convert to one unit (usually mg and mL) before you start.
- Estimate first. If you expect "a few mL" and get 90 mL, something's off.
- Watch for the salt versus base, and mmol versus mEq, wording.
- Practise with a timer. In the real exam you want calculations done in under two minutes each.
More calculation types to practise
Infusion rates. Convert the ordered dose to mg per hour, then divide by the bag concentration to get mL per hour. For mcg/kg/min orders, multiply by weight and by 60 before converting units. Example: 5 mcg/kg/min for a 70 kg patient is 350 mcg/min, or 21 mg/h. With a bag of 400 mg in 250 mL (1.6 mg/mL), the rate is 21 / 1.6 = 13.1 mL/h.
Alligation. When you mix a stronger and a weaker product to make a strength in between, the parts of each are the differences in the opposite corners. Mixing 10% and 2% to make 5%: 3 parts of 10% (5 minus 2) and 5 parts of 2% (10 minus 5), 8 parts in total.
Ratio strength. 1:1,000 means 1 g in 1,000 mL, which is 1 mg/mL. 1:10,000 is 0.1 mg/mL. Epinephrine questions often test exactly this.
Unit conversions. Vitamin D: 40 IU equals 1 mcg. Teaspoon dosing should always be converted to mL (5 mL per teaspoon) and given with an oral syringe.
Common traps
- Choosing the final volume when the question asks how much diluent to add.
- Using actual body weight for creatinine clearance when the question tells you to use ideal or adjusted weight.
- Using the wrong sex factor in Cockcroft-Gault (about 1.23 for men and 1.04 for women with creatinine in micromol/L).
- Mixing up mg and mmol, or mcg and mg, partway through.
- Rounding too early. Keep full figures until the last step.
Practise ten calculation questions
Our free PEBC calculation practice questions cover dilutions, alligation, infusion rates, mcg/kg/min doses and prescription quantities, with every step worked out and the trap behind each wrong option.
Common questions
How many calculation questions are on the PEBC MCQ? PEBC doesn't publish an exact count, but calculations appear across several competencies, especially clinical care and drug distribution. Expect a steady handful spread through the exam rather than one block.
Can I use a calculator? An on-screen calculator is provided on the computer-based exam. Practise with a basic calculator so you're not relying on scientific functions you won't have.
Which formula for creatinine clearance? Cockcroft-Gault is the one to know: (140 minus age) times weight in kg times a factor, divided by serum creatinine in micromol/L. The factor is about 1.23 for men and 1.04 for women. Read the question for which weight to use.
What's the fastest way to improve? Do ten calculations a day for two weeks, writing every unit. Most candidates who struggle aren't weak at maths; they skip steps.
Find out if calculations are a weak spot
The free RxReady diagnostic is 40 questions weighted like the exam. It shows your weakest topics, then your practice targets them.
Take the free diagnosticMore to read
A PEBC MCQ study plan that works
Canadian pharmacy law for the PEBC, including the new Controlled Substances Regulations
PEBC exam dates and deadlines for 2027