PTCE Cheat Sheet: Conversions and Key Pharmacy Math Formulas

PTCE math is mostly setup and units.

Yes, you need to calculate. But on the Pharmacy Technician Certification Exam, many math mistakes happen before the calculator ever matters.

Students often miss questions because they:

• Converted too late

• Used the wrong unit

• Mixed mg and mcg

• Confused daily dose with total quantity

• Used the wrong final volume

• Forgot that U-100 insulin means 100 units per mL

The calculator can handle arithmetic.

Your job is to know what to convert, how to set up the problem, and how to check whether the answer makes sense.

Use this as a study cheat sheet before the PTCE. Do not bring notes into the exam. PTCB provides a built-in calculator, and personal calculators are not allowed except under specific test-center conditions described by PTCB.

Convert Cleanly

Before you calculate, make the units match.

A good PTCE math order is:

1. Convert

2. Set up

3. Calculate

4. Check units

That order prevents most avoidable pharmacy math errors.

Metric Ladder

Know the common metric ladder:

• 1 kg = 1,000 g

• 1 g = 1,000 mg

• 1 mg = 1,000 mcg

This matters because medication strengths often move between grams, milligrams, and micrograms.

For example:

0.5 g = 500 mg

250 mcg = 0.25 mg

The trap is assuming the number is the hard part. Usually, the unit is the hard part.

Liquid Metric

Know:

1 L = 1,000 mL

This conversion shows up in liquid medications, IV volumes, compounding, and concentration problems.

Example:

0.25 L = 250 mL

If the final answer asks for mL, convert liters before calculating.

Household To Metric

Common pharmacy study conversions include:

• 1 tsp = 5 mL

• 1 tbsp = 15 mL

• 1 fl oz = about 30 mL

Technically, 1 U.S. fluid ounce is about 29.57 mL, but pharmacy math problems commonly use 30 mL unless a question gives a more specific conversion.

Also remember:

1 tbsp = 3 tsp

So:

1 tbsp = 15 mL

and

3 tsp = 15 mL

Weight And Temperature

For weight:

kg = lb ÷ 2.2

Example:

154 lb ÷ 2.2 = 70 kg

For temperature:

°C = (°F - 32) × 5/9

°F = (°C × 9/5) + 32

Weight matters for weight-based dosing. Temperature matters for storage, conversions, and certain medication handling questions.

Prescription Math

Prescription math is where setup matters most.

Do not rush to multiply numbers until you know what the question is asking.

Daily Dose

Formula:

Daily amount = dose × times per day

Example:

A patient takes 1 tablet twice daily.

1 tablet × 2 times daily = 2 tablets per day

If the prescription says 2 capsules three times daily:

2 capsules × 3 = 6 capsules per day

Always translate the sig before calculating.

Days Supply

Formula:

Days supply = quantity dispensed ÷ daily amount

Example:

Quantity dispensed: 60 tablets
Directions: 1 tablet twice daily

Daily amount:

1 × 2 = 2 tablets per day

Days supply:

60 ÷ 2 = 30 days

The key is to calculate the daily amount first.

Quantity To Dispense

Formula:

Quantity = dose × frequency × days

Example:

Directions: 1 tablet twice daily for 10 days

1 × 2 × 10 = 20 tablets

Be careful: this shortcut works cleanly when the dose is already expressed in the final dosage unit, such as tablets or capsules.

For liquids, you may need to calculate mL per dose first using the medication concentration.

Weight-Based Dose

Formula:

Dose = mg/kg × kg

Example:

Order: 10 mg/kg
Patient weight: 25 kg

10 × 25 = 250 mg

Then check the wording:

• Is that per dose?

• Is that per day?

• How many doses per day?

• Does the final answer need mg, mL, tablets, or total quantity?

Weight-based questions often have more than one step.

Strength And Dilution

These formulas help with concentration, reconstitution, percent strength, dilution, and insulin calculations.

Concentration

Formula:

mg/mL = total mg ÷ total mL

Example:

A bottle contains 250 mg in 5 mL.

250 ÷ 5 = 50 mg/mL

Once you know the concentration, you can calculate how many mL are needed for a dose.

Reconstitution

Formula:

Final concentration = drug amount ÷ final volume

The important phrase is final volume.

If a powder is mixed with diluent, the final volume may not always equal the diluent volume. Use the final volume given in the question or on the label.

Example:

A reconstituted medication contains 500 mg in a final volume of 10 mL.

500 ÷ 10 = 50 mg/mL

Percent Strength

Percent strength depends on the type of product.

For weight/volume:

% w/v = grams per 100 mL

For weight/weight:

% w/w = grams per 100 g

Example:

A 5% w/v solution contains:

5 g per 100 mL

This is a common pharmacy math concept, especially for solutions and compounding-style questions.

Dilution

Formula:

C1 × V1 = C2 × V2

Use this when the amount of drug stays the same but concentration and volume change.

Where:

• C1 = starting concentration

• V1 = starting volume

• C2 = final concentration

• V2 = final volume

The most common mistake is solving for the wrong variable.

Before calculating, write what each part represents.

Insulin U-100

U-100 insulin means:

100 units per mL

Formula:

mL = units ordered ÷ 100 units/mL

Example:

Order: 25 units

25 ÷ 100 = 0.25 mL

Insulin questions are safety-sensitive. Always check the unit, concentration, and syringe wording carefully.

How To Avoid PTCE Math Mistakes

Use this checklist:

• Convert units before calculating

• Match the final answer unit

• Translate the sig carefully

• Calculate daily amount before days supply

• Use final volume for reconstitution

• Check whether weight-based dosing is per dose or per day

• Know that U-100 means 100 units/mL

• Use the calculator for arithmetic, not setup

• Check whether the answer size makes sense

A strange answer usually means the setup needs another look.

Final Takeaway

PTCE math is not about memorizing every possible problem.

It is about recognizing the setup.

Know these core tools:

• Metric conversions

• Household-to-metric conversions

• Pounds to kilograms

• Temperature formulas

• Daily dose

• Days supply

• Quantity to dispense

• Weight-based dose

• Concentration

• Reconstitution

• Percent strength

• Dilution

• U-100 insulin

The calculator helps with numbers.

But the score comes from the setup.

Convert first. Set up carefully. Calculate second. Check units last.

Educational note: This is independent PTCE study content, not pharmacy practice guidance. Always follow your training program, pharmacist supervision, workplace policies, state law, and PTCB rules.

Accuracy sources checked: PTCB PTCE Content Outline, PTCB CPhT Exam At-a-Glance, PTCB Calculator Policy, OpenStax Dosage Calculations, NCBI StatPearls Pharmacy Calculations, and Merck Manual Conversion Table.