Pharmacy Conversions for PTCE Math: Chart, Examples, and Practice

Last reviewed July 17, 2026.

Pharmacy conversions change a measurement from one unit to another. Examples include grams to milligrams, liters to milliliters, or pounds to kilograms. If you’re studying for the Pharmacy Technician Certification Examination (PTCE), you need the core metric relationships and a repeatable way to set up each question so the unit you start with cancels.

The Pharmacy Technician Certification Board (PTCB) publishes the PTCE content outline. Its current outline includes conversions in Order Entry and Processing, although it does not assign a specific number of questions to conversions.

This page covers unit math. It does not compare one medication with another or tell you what dose is right for a patient.

Use the conversion factor provided in the question. If none is provided, use exact metric relationships and treat rounded U.S. customary values as study shortcuts.

Table of Contents

• What to Memorize First for PTCE Practice
• Pharmacy Conversion Chart
• How to Choose and Set Up a Conversion Factor
• Worked Pharmacy Conversion Examples
• Common Conversion Mistakes and Quick Fixes
• Pharmacy Conversion Practice Questions
• A Five-Minute Study Routine
• Pharmacy Conversions FAQ

What to Memorize First for PTCE Practice

Learn these four metric relationships first:

• 1 kg = 1,000 g
• 1 g = 1,000 mg
• 1 mg = 1,000 mcg
• 1 L = 1,000 mL

They are exact, and each step changes by a factor of 1,000. When you move to a smaller unit, multiply by 1,000. When you move to a larger unit, divide by 1,000.

What to memorize: the four metric relationships above.

What to use when the question supplies it: rounded factors for pounds, fluid ounces, tablespoons, teaspoons, and the temperature formula.

What to keep consistent: use the same factor from the setup through the final answer.

Rounded values can differ slightly among courses and practice materials. That is why the factor printed in the question takes priority over a value you remember from another source.

Pharmacy Conversion Chart

Metric mass and volume

These exact relationships follow the SI prefix system explained in NIST Special Publication 811.

Takeaway: The same quantity needs a larger number of smaller units and a smaller number of larger units.

For example, 750 mg equals 0.75 g. The unit became larger, so the number became smaller.

Common weight and volume study factors

Questions that move between U.S. customary and metric units are best solved using a rounded factor. The study setups below are common shortcuts. The more precise reference values come from NIST’s conversion tables and explain why answers can differ slightly when different factors are used.

Takeaway: A rounded setup is a study shortcut, not an exact measurement. If a question supplies a different factor, use that factor from start to finish.

A fluid ounce measures volume. An ounce without “fluid” usually refers to mass, so don’t treat oz and fl oz as interchangeable.

Medication-measurement note: The 5 mL teaspoon value is useful in study questions, but a household spoon is not a dosing tool. The FDA warns that household spoons vary widely in volume. For an actual medication, follow the label and use a measuring device marked in milliliters. Ask a pharmacist or another qualified clinician if the directions or device are unclear.

Temperature and time

• Fahrenheit to Celsius: °C = (°F − 32) × 5/9
• Celsius to Fahrenheit: °F = (°C × 9/5) + 32
• Hours to minutes: 1 hour = 60 minutes
• Days to hours: 1 day = 24 hours

Use the temperature formula provided by the question when it gives one. The NIST quick-reference conversion card lists the temperature relationships alongside common weight and volume conversions.

How to Choose and Set Up a Conversion Factor

Choose your factor in this order:

1. Use the factor supplied in the question. It determines the setup and rounding the question requires.
2. Otherwise, use an exact metric relationship. Examples include 1 g = 1,000 mg and 1 L = 1,000 mL.
3. Use a rounded study factor only when your course or practice question expects one. Examples include 1 kg ≈ 2.2 lb and 1 fl oz ≈ 30 mL.

Once you have the factor, use this dimensional-analysis template:

amount you have × (unit you want / unit you have) = converted amount

Put the unit you want on top and the unit you already have on the bottom. The unit you started with should cancel, leaving only the unit requested in the question.

For example, convert 0.75 g to mg:

0.75 g × (1,000 mg / 1 g) = 750 mg

• Have: grams
• Want: milligrams
• Factor: 1,000 mg / 1 g
• Unit check: grams cancel and milligrams remain
• Size check: milligrams are smaller than grams, so the number should grow

If the starting unit does not cancel, turn the conversion factor over before doing the arithmetic.

Worked Pharmacy Conversion Examples

1. Convert grams to milligrams

Question: Convert 1.25 g to mg.

1.25 g × (1,000 mg / 1 g) = 1,250 mg

The unit became smaller, so the number became larger.

2. Convert micrograms to milligrams

Question: Convert 2,500 mcg to mg.

2,500 mcg × (1 mg / 1,000 mcg) = 2.5 mg

The unit became larger, so the number became smaller.

3. Convert milliliters to liters

Question: Convert 625 mL to L.

625 mL × (1 L / 1,000 mL) = 0.625 L

Liters are larger than milliliters, so the numerical answer should be smaller.

4. Convert pounds to kilograms

Question: Convert 154 lb to kg using 2.2 lb = 1 kg.

154 lb × (1 kg / 2.2 lb) = 70 kg

Because the question uses a rounded factor, 70 kg is an approximate result.

5. Convert U.S. fluid ounces to milliliters

Question: Convert 8 fl oz to mL using 1 fl oz ≈ 30 mL.

8 fl oz × (30 mL / 1 fl oz) = 240 mL

Because the question uses a rounded factor, 240 mL is an approximate result.

6. Convert Fahrenheit to Celsius

Question: Convert 68°F to Celsius.

(68 − 32) × 5/9 = 20°C

Temperature conversions need the full formula because the Fahrenheit and Celsius scales have different zero points.

7. Complete a two-step metric conversion

Question: Convert 0.002 kg to mg.

0.002 kg × (1,000 g / 1 kg) × (1,000 mg / 1 g) = 2,000 mg

Kilograms and grams cancel in sequence, leaving milligrams. Because milligrams are much smaller than kilograms, the number should grow substantially.

Common Conversion Mistakes and Quick Fixes

Flipping the factor

If the starting unit does not cancel, the factor is facing the wrong direction. Turn it over before calculating.

Moving the decimal without checking direction

Ask whether the requested unit is smaller or larger. The same quantity needs a larger number of smaller units and a smaller number of larger units.

Dropping units from the setup

Keep the units beside every number. They show whether the factor is oriented correctly and which unit should remain in the answer.

Mixing rounded and more precise factors

Choose one factor and use it throughout the question. Switching factors halfway through can change the final result.

Confusing mass with volume

Pounds, grams, and milligrams measure mass. Liters, milliliters, and U.S. fluid ounces measure volume. You cannot convert directly between mass and volume without additional information, such as a concentration or density.

Rounding too early

Keep extra digits until the final step unless the question gives different instructions. Early rounding can move a multi-step answer farther from the expected result.

Pharmacy Conversion Practice Questions

Use the chart during your first round. During your second round, cover the relationship column and work from memory. Write the units on every line.

Core metric practice

1. Convert 0.42 g to mg.
2. Convert 3,600 mcg to mg.
3. Convert 850 mg to g.
4. Convert 2.75 L to mL.
5. Convert 625 mL to L.
6. Convert 176 lb to kg using 2.2 lb = 1 kg.
7. Convert 2.5 kg to lb using 1 kg ≈ 2.2 lb.
8. Convert 6 U.S. fl oz to mL using 1 fl oz ≈ 30 mL.
9. Convert 3 Tbsp to mL using 1 Tbsp ≈ 15 mL.
10. Convert 95°F to Celsius.
11. Convert 2.5 hours to minutes.
12. Convert 0.002 kg to mg.
13. A question tells you to use 1 fl oz = 29.57 mL. Should you use 29.57 or the rounded value 30?
14. Can you convert 250 mg directly to mL using only the unit relationships on this page?

Show the answer key

1. 0.42 g × (1,000 mg / 1 g) = 420 mg
2. 3,600 mcg × (1 mg / 1,000 mcg) = 3.6 mg
3. 850 mg × (1 g / 1,000 mg) = 0.85 g
4. 2.75 L × (1,000 mL / 1 L) = 2,750 mL
5. 625 mL × (1 L / 1,000 mL) = 0.625 L
6. 176 lb × (1 kg / 2.2 lb) = 80 kg approximately
7. 2.5 kg × (2.2 lb / 1 kg) = 5.5 lb approximately
8. 6 fl oz × (30 mL / 1 fl oz) = 180 mL approximately
9. 3 Tbsp × (15 mL / 1 Tbsp) = 45 mL approximately
10. (95 − 32) × 5/9 = 35°C
11. 2.5 hours × (60 minutes / 1 hour) = 150 minutes
12. 0.002 kg × (1,000 g / 1 kg) × (1,000 mg / 1 g) = 2,000 mg
13. Use 29.57 because it is the factor supplied in the question.
14. No. A direct mass-to-volume conversion needs additional information, such as a concentration or density.

If you miss a question, label the cause before trying it again: wrong factor, flipped factor, arithmetic, rounding, or missing unit. Redo that type with new numbers instead of copying the answer.

A Five-Minute Study Routine

1. Minute 1: Write the four core metric relationships from memory.
2. Minute 2: Point to each pair and say which direction multiplies and which divides.
3. Minute 3: Solve one conversion to a smaller unit and one to a larger unit.
4. Minute 4: Solve one question that converts between U.S. customary and metric units, or solve one temperature question using the formula provided.
5. Minute 5: Check the units, estimate whether the answer should grow or shrink, and record any mistake.

Your next step is to repeat the missed question type the next day with different numbers. Short retrieval sessions will tell you more about what you know than rereading the chart without solving anything.

For a broader exam plan, use the PTCE study guide. When you’re ready to mix conversions with other topics, try the free mixed-topic practice test.

Pharmacy Conversions FAQ

Do I need to memorize every conversion for the PTCE?

Start with the four exact metric relationships, then learn how to build a conversion factor and follow any factor supplied in the question. The PTCB outline includes conversions but does not say how many questions will test them.

Are pharmacy conversions the same as dosage calculations?

No. A unit conversion changes how a quantity is expressed. It may be one step within a larger calculation, but it does not select a medication or determine whether a patient-specific dose is appropriate.

Sources for This Guide

• NIST Special Publication 811 — SI units, prefixes, and conversion conventions.
• NIST Appendix B.8 — reference values for U.S. customary and metric conversions.
• NIST’s quick-reference conversion card — common weight, volume, and temperature relationships.
• FDA guidance on liquid medication measurement — why household spoons should not be used as medication-measuring tools.
• PTCB’s current PTCE Content Outline — the current exam content domains.