Units of Measurement
Units of Measurement
The United States uses customary units, sometimes called standard units. In this system, several different units can be used to describe the same variable. These units and the relationships between them are shown in Table 3.6.
US Customary Units | ||
|---|---|---|
Variable Measured | Unit | Conversions |
Length | inches, foot, yard, mile | 12 inches = 1 foot 3 feet = 1 yard 5280 feet = 1 mile |
Weight | ounces, pound, ton | 16 ounces = 1 pound 2000 pounds = 1 ton |
Volume | fluid ounces, cup, pint, quart, gallon | 8 fluid ounces = 1 cup 2 cups = 1 pint 2 pints = 1 quart 4 quarts = 1 gallon |
Time | second, minute, hour, day | 60 seconds = 1 minute 60 minutes = 1 hour 24 hours = 1 day |
Area | square inch, square foot, square yard | 144 square inches = 1 square foot 9 square feet = 1 square yard |
Most other countries use the metric system, which has its own set of units for variables like length, weight, and volume. These units are modified by prefixes that make large and small numbers easier to handle. These units and prefixes are shown in Table 3.7.
Metric Units and Prefixes | |
|---|---|
Variable Measured | Base Unit |
length | meter |
weight | gram |
volume | liter |
Metric Prefix | Conversion |
kilo | base unit × 1000 |
hecto | base unit × 100 |
deka | base unit × 10 |
deci | base unit × 0.1 |
centi | base unit × 0.01 |
milli | base unit × 0.001 |
Conversion factors are used to convert one unit to another (either within the same system or between different systems). A conversion factor is simply a fraction built from two equivalent values. For example, there are 12 inches in 1 foot, so the conversion factor is \(\frac{12\ in}{1\ ft}\) or \(\frac{1\ ft}{12\ in}\).
To convert from one unit to another, multiply the original value by a conversion factor. Choose a conversion factor that will eliminate the unwanted unit with the desired unit.
How many inches are in 6 feet?
\(6\ ft\ ×\ \frac{12\ in}{1\ ft} = \frac{6\ ft\ ×\ 12\ in}{1\ ft} = 72\ in\)