Pharmacy Math: Unit Conversions Every Tech Must Master

Why Unit Conversions Matter

Pharmacy technicians constantly convert between measurement systems when processing prescriptions, compounding medications, and performing calculations. The PTCE tests your ability to convert accurately between metric, apothecary, and household systems. Mastering these conversions eliminates careless errors.

Metric System Essentials

The metric system is the standard in pharmacy:

• Weight: 1 kg = 1,000 g; 1 g = 1,000 mg; 1 mg = 1,000 mcg
• Volume: 1 L = 1,000 mL
• Move the decimal point three places when converting between adjacent metric units

Household to Metric Conversions

• 1 teaspoon (tsp) = 5 mL
• 1 tablespoon (tbsp) = 15 mL
• 1 fluid ounce (fl oz) = 30 mL
• 1 cup = 240 mL
• 1 pint = 473 mL (approximately 480 mL)
• 1 pound (lb) = 454 g
• 1 kg = 2.2 lb

Apothecary Conversions

• 1 grain (gr) = 65 mg (approximately)
• Apothecary units are becoming rare but still appear on older prescriptions and on the PTCE

Temperature Conversions

Important for medication storage requirements:

• Fahrenheit to Celsius: C = (F - 32) x 5/9
• Celsius to Fahrenheit: F = (C x 9/5) + 32
• Room temperature: 20-25 degrees C (68-77 degrees F)
• Refrigerator: 2-8 degrees C (36-46 degrees F)
• Freezer: -25 to -10 degrees C (-13 to 14 degrees F)

Dimensional Analysis Method

Dimensional analysis is the most reliable method for complex conversions. Set up your equation so unwanted units cancel out. Example: Convert 150 lb to kg. 150 lb x (1 kg / 2.2 lb) = 68.2 kg. The "lb" units cancel, leaving kg.

Practice conversions daily until they are automatic. Try our PTCB math practice problems for timed drills.