The Metric System¶
Why Metric?¶
The metric system is the international standard for medication dosing and clinical measurement. Unlike household measurements, the metric system is decimal-based — everything scales by powers of 10, making conversions straightforward.
Base Units in Nursing¶
| Measurement | Base Unit | Abbreviation |
|---|---|---|
| Weight | gram | g |
| Volume | liter | L |
| Length | meter | m |
Prefixes¶
Prefixes modify the base unit by a power of 10:
| Prefix | Symbol | Meaning | Example |
|---|---|---|---|
| kilo | k | × 1000 | 1 kg = 1000 g |
| (base) | — | × 1 | 1 g |
| milli | m | × 0.001 | 1 mg = 0.001 g |
| micro | mc or µ | × 0.000001 | 1 mcg = 0.001 mg |
Memory Tip
Think of it as a staircase — each step down multiplies by 1000:
Moving down the staircase (larger to smaller unit) — multiply by 1000
Moving up the staircase (smaller to larger unit) — divide by 1000
Key Weight Conversions¶
[1 \text{ kg} = 1000 \text{ g}] [1 \text{ g} = 1000 \text{ mg}] [1 \text{ mg} = 1000 \text{ mcg}]
Key Volume Conversions¶
[1 \text{ L} = 1000 \text{ mL}] [1 \text{ dL} = 100 \text{ mL}]
Abbreviation Safety¶
mcg vs mg
Never abbreviate microgram as µg in handwritten orders — it can be misread as mg, resulting in a 1000x overdose. Always write mcg in full.
Units of Insulin
Never abbreviate units as U for insulin orders. U can be misread as a zero, turning 4U into 40 units. Always write units in full.
Clinical Application¶
Example 1: A medication order reads 0.5 g. Stock is labeled in mg. What is the equivalent dose in mg?
Example 2: A patient weighs 75 kg. A weight-based dose requires the weight in grams. Convert:
Example 3: A lab value is reported as 1500 mcg. Convert to mg:
Practice Problems¶
Problem 1
Convert 2.5 g to mg.
Answer
Problem 2
Convert 750 mg to g.
Answer
Problem 3
Convert 0.25 mg to mcg.
Answer
Problem 4
Convert 2500 mL to L.
Answer
Problem 5
An order reads 0.125 mg. Stock is labeled in mcg. What is the equivalent dose?
Answer
Clinical Tip
When converting between metric units always ask yourself — am I going to a smaller or larger unit? Smaller unit = larger number. Larger unit = smaller number. If your answer goes the wrong direction, recheck your work.