# 5.1 Using Units of Measurement

Everyday problems often involve measurements, where you want to determine how much there is of some quantity. Things are measured to find out how big, how long, or how heavy they are. For these numbers to have any meaning, you need to specify what units the measurement is in. For example, there’s a big difference between 3 feet and 3 miles!

Although most of the scientific world has adopted an agreed-upon system of measurement, the United States still uses its own system, which is closely related to what is called the Imperial system. The internationally agreed units, and the rules for their use, form the Système Internationale (International System), known as SI, which uses metric units.

As you may encounter both systems of measurement in your daily life, we will look at each in this section.  Even if you don’t use the US system, the activities in the section are still good practice at converting between different units of measurement and problem solving—so give them go!

5.0.1 What to Expect in this Unit

5.1.1 Length Measurements