Why Metric Conversions Matter
Metric conversions are fundamental to pharmacy calculations. Nearly every dosage calculation, compounding formula, or IV preparation involves working with metric units. Fluency with conversions saves time on the PTCE and prevents errors in daily practice.
The Basic Metric Units
- Weight: grams (g), milligrams (mg), micrograms (mcg), kilograms (kg)
- Volume: liters (L), milliliters (mL)
- Length: meters (m), centimeters (cm) - less common in pharmacy
Key Conversion Relationships
- 1 kg = 1,000 g
- 1 g = 1,000 mg
- 1 mg = 1,000 mcg
- 1 L = 1,000 mL
Metric to Household Conversions
You also need to convert between metric and household measurements:
- 1 teaspoon (tsp) = 5 mL
- 1 tablespoon (tbsp) = 15 mL
- 1 fluid ounce (fl oz) = 30 mL
- 1 pound (lb) = approximately 454 g
- 1 kg = 2.2 lb
Conversion Technique
The safest way to convert is by moving the decimal point or using a proportion. When converting from a larger unit to a smaller unit (grams to milligrams), multiply. When converting from a smaller unit to a larger unit (milligrams to grams), divide. Practice until these conversions feel automatic.
Common Exam Scenarios
You might be asked to convert a dose from milligrams to grams, determine how many milliliters are in a certain number of teaspoons, or convert a patient's weight from pounds to kilograms for a weight-based dosing calculation. Each of these uses the same basic conversion relationships listed above. Practice with varied problems until the process becomes second nature.