Measurement Units and Conversions for Medications
• Memorize the units of metric measurement used in medication orders.
• State equivalent values of weight (mass) and volume used in metric dose calculations: micrograms, milligrams, grams, kilograms, milliliters, and liters.
• Distinguish milligram, milliliter, and milliequivalent.
• Define the uses of the term Unit related to measurements and medications.
• Calculate basic metric oral medication problems using mental arithmetic and decimal placement.
• Verify metric conversions using dimensional analysis.
• Use approved abbreviations for metric units.
Introduction
Modern metric measurements have almost completely replaced an old English imprecise Apothecary system* in order to reduce medication errors. The modern metric system is logical, precise, and easy to work with because it’s a standardized decimal measurement system using multiples (powers) of 10 similar to our monetary structure which is also based on a decimal structure. With a little practice and repetition, nurses will be very comfortable with it.
This chapter focuses on understanding and interpreting the metric measurements used in medication orders and records, on medication labels, in laboratory reports, and nursing practice. It also includes examples of household measurements. Household measures are used for some medications taken at home, primarily liquids. Nurses need to know the metric-household equivalents for home care practice, for patient and family discharge and home-care teaching. Teaspoon A does not equal teaspoon B.
Base Units of Metric Measurement Three base units are commonly used for metric measurement of medications to indicate weight (or mass), volume, and length: gram (g), liter (L), and meter (m).
Memorize these base units of measurement. The abbreviation for liter is preferably capitalized, L, to avoid confusion with the number 1.
Household System of Measurement Utensils used in the home, such as cups, teaspoons, tablespoons, droppers, etc. Their use can create a safety risk for measuring medication doses because of inconsistent capacities.
ISMP Institute for Safe Medication Practices, a non-profit organization that educates the health care community and consumers about safe medication practices.
Modern Metric System A popular name for the International System of Units (SI). Modified and adopted for uniform measurement in most countries, now recommended for all medication doses in the US by TJC and by ISMP.
SI Units SI Units in the metric system refer to a dimension, such as weight (or mass), volume, and length. Examples of metric units of measurement include kilogram (kg), microgram (mcg), milligram (mg), gram (g), liter (L), and meter (m). 
Write out the words unit and units; do not use abbreviations such as U.
TJC The Joint Commission, a national non-profit independent agency dedicated to improved quality of health care through the provision of accreditation and certification to health care organizations with an emphasis on high standards and patient safety including medication administration safety.
| Weight | Volume |
| 1000 mcg (micrograms) = 1 mg (milligram) | 1000 mL (milliliter) = 1 L (liter) |
| 1000 mg = 1 g (gram) | |
| 1000 g = 1 kg (kilogram) | |
| Length | |
| lb to kg conversion | 10 mm (millimeters) = 1 centimeter (cm) |
| 2.2 lb (pound) = 1 kg | 100 cm = 1 meter (m) |
| inch to cm conversion | 1000 mm = 1 meter (m) |
| 1 inch = 2.5 cm (approximate) |
Metric Measurements: Base Units
Three base units are commonly used in the medical field. Two are used mainly for medication doses (gram and liter) and one (meter) is used occasionally for topical medications.
| Dimension | Metric Base Unit | Approximate English System Equivalent |
| Weight (or mass) | gram (g) | About  ounce dry weight |
| Volume | liter (L) | About 4 measuring cups, a little more than a quart |
| Length | meter (m) | About 39 inches, a little more than a yard |
The abbreviation for the base unit liter is capitalized (L) to avoid misreading as the number 1. The base units abbreviations for gram (g) and meter (m) are written in lowercase letters. No other abbreviations are authorized.
1. What are the three base units of metric measurement used for medications and their abbreviations?
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Metric Prefixes and Values
Four prefixes are commonly used for medication dose calculations:
• kilo- (meaning a thousand times)
• A fifth prefix, deci- (meaning tenth), is used in laboratory reports.
Study Table 3-1, and note the numerical values and relationships. Metric prefixes are combined with bases to create new quantities, as shown in the examples in the table.
TABLE 3-1
Metric Measurements, Prefixes, Values, and Meaning
| Prefix | Multiplier | Exponential Power of 10 | Meaning | Examples | Meaning |
| micro (mc) | .000001 | 10−6 | millionth part of | microgram (mcg) | one millionth of a gram |
| milli (m) | .001 | 10−3 | thousandth part of | milliliter (mL) | one thousandth of a liter |
| milligram (mg) | one thousandth of a gram | ||||
| centi (c) | .01 | 10−2 | hundredth part of | centimeter (cm) | one hundredth of a meter |
| deci- (d) | .1 | 1 0−1 | tenth part of | deciliter (dL) | one tenth of a liter |
| kilo- (k) | 1000 | 10−3 | 1000 times | kilogram (kg) | one thousand grams |
Note: The prefix value never changes when combined with a base unit (e.g., the prefix milli [m] = 001).
1 mm = 0.001 (one thousandth of a meter).
1 mL = 0.001 (one thousandth of a liter).
1. What are the numerical values of the prefixes m, c, d, and k?
_________________________________________________________________________
• For review, write out the five prefixes and three base units used for medication administration. Learn them in preparation for analyzing medication orders.
| Prefixes and Abbreviations | Base Units and Abbreviations |
The abbreviation for the prefix micro (mc) is preferred over the Greek letter mu (μ) in handwritten patient medical records. A handwritten μg (microgram) can be mistaken for mg (milligram).
RAPID PRACTICE 3-2 Writing Metric Units and Abbreviations
Estimated completion time: 10 minutes Answers on page 492
1. Write the name and abbreviation for the prefix that means 
__________
2. Write the name and abbreviation for the prefix that means 
_______
3. Write the name and abbreviation for the prefix that means 
_______
4. Write the name and abbreviation for the prefix that means 
_______
5. Write the name and abbreviation for the prefix that means 1000 times. _______
6. Write the name and abbreviation for the base unit of volume. _______
7. Write the name and abbreviation for the base unit of length. _______
8. Write the name and abbreviation for the base unit of weight, or mass. _______
9. Write the name for the base unit m. _______
Metric Notation
Writing metric unit combinations and equivalents
Study the example and note the correct order of writing as follows:
Do not write an m to look like a w or a u.
Metric abbreviations are case sensitive.
Do not close up a c so that cm looks like am.
Do use commas to group numbers with more than three consecutive zeros in groups of three from right to left.
Do not make up your own metric abbreviations
| Guide to Metric Notation | Examples |
| Abbreviations are always used when accompanied by a number. The number, followed by a space, precedes the abbreviation. | 10 mg, 2 g, 5 L |
| Metric terms are written out when unaccompanied by a number, as illustrated in the following sentence: “Write out grams and milligrams.” | |
| When the number of units following the slash meaning per is 1, the number 1 may be omitted from the abbreviation. It is implied. | 40 mg/ g (40 mg per 1 g) |
| Metric abbreviations are always singular. They are not pluralized. | Milligrams is abbreviated mg. |
| Liters is abbreviated L. | |
| Write mg, not mgs; g, not gs; and L, not Ls. | |
| There is no period after metric abbreviations except when they fall at the end of a sentence. | Give 2 mg, not 3 mg. |
| He drank 2 L of water, followed by 1 L. |
Slashes appear in many drug and laboratory references. The nurse must be able to interpret them. Do not write them. They have been mistaken for the number one (1). The word “per” is to be written out instead of a slash. Refer to the ISMP list of symbols that lead to medication errors on p. 103.
1. Are there 100 or 1000 cm in a meter?
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2. Are there 100 or 1000 mg in a gram?
______________________________________________________________________
3. Are there 10 or 100 dL in a liter?
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RAPID PRACTICE 3-6 Metric Base Units
Estimated completion time: 5 minutes Answers on page 492
Directions: Write the requested metric base units in the correct form in the space provided.
1. Which metric base unit abbreviation presented in this chapter must be capitalized? ______
2. Which metric base unit abbreviation would be added to the prefix c in a measurement of the length of a scar? ______
3. Which metric base unit abbreviation would be added to the prefix m in a measurement of fluids consumed? ______
4. Which metric base unit abbreviation would be added to the prefix k in a measurement of current weight? ______
5. Which metric base unit abbreviation would be added to the prefix m in a measurement of drug weight? ______
Read the labels on food, beverages, medicines, and vitamins to speed learning of the uses of g and mg.
1. The average American consumes about 5 g of sodium per day. Intake should be restricted to about 2 g of sodium from all sources. 1 tsp of table salt (NaCl) contains 2300 mg of sodium. Approximately how many grams of sodium do you consume on an average day?
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