6 Common Units in Nursing


Learning Outcomes

By the end of this chapter, learners will be able to:

  • identify common units of measurement for amount, mass and liquid volume in the metric system, and
  • identify the correct abbreviations for common units of measure.

Understanding the Metric System

Types of Units

It’s likely you have learned about the metric system (also known as The International System of Units) at some point in your past education, but perhaps some of the details are a little fuzzy. There are seven basic types of measure, which relate to quantities of time, length, mass, electric current, thermodynamic temperature, amount of substance and luminous intensity (National Institute of Standards and Technology, 2020). However, we will focus on only four types, as they are the measurements most commonly used in nursing. The mole, grams, metres and litres. Respectively, these units measure amount of a substance, mass (weight), length and volume (capacity).


Difference Between Volume and Capacity

You might think of litres as a way to measure the volume of a liquid, but it’s not the most precise definition. Volume is a measure of how much space an object takes up, always measured in cubic units, such as cubic centimetres. Can you remember calculating the volume of objects in high school geometry? Multiplying the height, width and length of an object would give the volume of the object. Capacity is the measurement of how much of a substance can be inside an object, which could be matter existing in any state. Although there are many units to measure capacity, litre is most commonly used unit for measuring liquid matter. For use in nursing work, litre is commonly referred to as a measure of volume.

Base Units and Sizes of Measurements

When units of measure go up and down in size, they do so by a power of ten. A prefix is added to the base unit to indicate the size of the unit. For instance, a unit ten times larger than a gram is a decagram. You will not often see all of the possible units of measure being used in nursing work, so for the purposes of this text we will focus on the units you will use most often.

Table 6.1 Common Base Units
Metric Prefix Symbol Power of 10 Meaning Multiply By
tera T 1012 one trillion 1,000,000,000,000
giga G 109 one billion 1,000,000,000
mega M 106 one million 1,000,000
kilo k 103 one thousand 1,000
hecto h 102 one hundred 100
deca da 101 ten 10
deci d 10−1 one tenth 1/10
centi c 10−2 one hundredth 1/100
milli m 10−3 one thousandth 1/1,000
micro μ 10−6 one millionth 1/1,000,000
nano n 10−9 one billionth 1/1,000,000,000
pico p 10−12 one trillionth 1/1,000,000,000,000

Commonly Used Units

The following table outline units which are commonly used in medication orders and in medication administration in Canada. You should understand what these units measure and how to convert from one unit of measure to another. Occasionally, you will see measurements given using the US customary system of measure, derived from the British imperial system of measure. You may need to convert between units of the metric and imperial systems of measurement. Refer to the conversion table in this textbook for commonly used conversion factors.

Table 6.2 Common Units
Quantity Abbreviation Measure
Amount i.u. international unit
Amount mEq milliequivalent
Amount mmol millimole
Volume mL millilitre
Volume L litre
Mass mcg microgram
Mass mg milligram
Mass g gram
Mass kg kilogram
Length cm centimetre
Length m metre

Defining Units

Within the table above, each unit of measure is defined in the glossary of this textbook. Click on the word to view the definition if you are unable to define the unit of measure in your own words. If using this book in another format, you can find the glossary at the back of the book.

National Institute of Standards and Technology. (2020, January). SI units.

Practice Set 6.1: Unit Abbreviations

Practice Set 6.1: Unit Abbreviations



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A Guide to Numeracy in Nursing Copyright © 2023 by Julia Langham is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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