Giving medicines requires the nurse to use precise weights and measures so each dose is the same. General household measures are often used when medicine is given in the home; unfortunately, it is not very accurate but patients are familiar with it. For example, 1 glass equals 8 ounces. Although one would think that this system is out of date for giving current medications, LPNs/LVNs practice in a wide variety of settings and may need to know this information. It is also important to understand household measures because this may be what patients will use in talking with you about how much medication they take. Household measures you should know are listed in Box 8-1.

Box 8-1

Common Equivalents

Common Household Equivalents

1 teaspoon = approximately 5 mL

1 tablespoon = 3 teaspoons

1 cup = 8 ounces

1 pint = 2 cups

1 quarter = 4 cups

Another measuring system is the apothecary system that was used primarily by pharmacists. This system is no longer recommended for use but a few medications have survived that are listed in grains (aspirin, iron, quinidine), and drops (gtts) are used in intravenous calculations. Drams and minims are no longer used. 1 grain = 60 or 64 mg of 0.06 g; 1/60 grain = 1 mg

• To convert grains to grams, divide by 15 or 16. To convert grams to milligrams, move the decimal point three places to the right. To convert grams to grains, multiple by 15 or 16.

• To convert grains to milligrams, multiple by 60 or 64. To convert milligrams to grams, move the decimal point three places to the left. To convert milligrams to grains, divided by 60 or 64.

Metric System

The metric system was developed in France and relies on a decimal system; it is built on multiples of 10 (tens, hundreds, and thousands). The metric system is the most commonly used drug measurement system. The metric system is the main system used internationally to measure weight, length, and volume.

The metric system uses meter (m) for the unit of length, liter (L) for the unit of volume, and gram (g) for the unit of weight. The most common measures used in the metric system are listed in Box 8-2.

Memory Jogger

Common Metric Equivalents

Milliliters, cubic centimeters, and grams are approximately equivalent; 1 mL, or 1 cc, weighs approximately 1 g.

Relying on what you know about the decimal system, it is simple to change measures within the metric system. To change milligrams to micrograms, move the decimal point three places to the right (multiply by 1000):