Understanding Metric vs Apothecary Systems

Introduction

Pharmacy technicians must navigate multiple measurement systems with precision. The Metric and Apothecary systems are two of the most common—but mixing them can lead to serious errors. This guide helps you understand the differences, recognize common conversions, and avoid dangerous mix-ups.

Section 1: Metric System Basics

• Used globally in healthcare and science
• Based on units of 10 (easy to convert)
• Common units:
  • Volume: milliliter (mL), liter (L)
  • Weight: milligram (mg), gram (g), microgram (mcg)

Section 2: Apothecary System Overview

• Older system, still seen in some prescriptions
• Units are non-decimal, harder to convert
• Common units:
  • Volume: minim, fluid dram, fluid ounce
  • Weight: grain (gr), scruple, dram

Section 3: Why Mixing Systems Is Risky

• 1 grain ≠ 1 gram (1 gr ≈ 64.8 mg)
• 1 fluid ounce ≠ 1 ounce (weight)
• Misinterpretation can lead to overdosing or underdosing

Section 4: Common Conversions

Technician Takeaway

Always confirm the system used in a prescription.
When in doubt, ask the pharmacist and double-check your math.
Precision isn’t optional—it’s your responsibility.