Converting Metric Units

Let's take a look at how to convert units of the metric system. You'll need to learn how to convert from one metric unit to another (e.g., grams to milligrams) in order to arrive at like units when calculating a dose. For example, if the dose is in milligrams and the prescriber's medication order specifies grams, you'll need to convert grams to milligrams before calculating the dose.

Converting from one metric unit to another metric unit isn't difficult if you remember these three rules.

1. Determine if the desired measurement is larger or smaller than the given measurement. Remember that gram, liter, and meter are larger units and milligram, milliliter, and millimeter are smaller units.

2. If you are converting from a smaller unit to a larger unit, then you multiply by moving the decimal three places to the left.

3. If you are converting from a larger unit to a smaller unit, then you divide by moving the decimal three places to the right.

Suppose the medication order is 300 mg and you need to convert this to grams. A milligram is smaller than a gram. You are converting from a smaller unit (a milligram) to a larger unit (a gram). Therefore, you divide by moving the decimal three places to the left, as shown here.

If the prescriber ordered 0.9 grams and the dose that you need is in milligrams, you are converting from a larger unit (a gram) to a smaller unit (a milligram). Therefore, you multiply by moving the decimal three places to the right, as shown here.

One of the most common conversions that you'll perform is converting milliliters into cubic centimeters. This is also the easiest conversion because one milliliter (mL) is equal to 1 cubic centimeter (cc).

Always place a zero to the left of the decimal when the quantity is not a whole number. This avoids errors when reading the number.

Incorrect: .9 Correct: 0.9

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