# 5.1.5 The Metric System

A meter is roughly equivalent to a yard. For longer lengths, such as the distance between two towns, the SI system uses a multiple of the base unit, a kilometer (km for short).

[ The “kilo” in kilometer is an example of a prefix—a letter or word placed in front of another word. ] “Kilo” means “a thousand”. This means that 1 kilometer is the same distance as a thousand meters.

There are other prefixes for smaller units. So, the width of your computer screen might be measured in centimeters (cm), where “centi” means “a hundredth”. So, there are 100 centimeters in 1 meter.

Centimeters are further divided into millimeters—as the name suggests, there are 1000 mm in a meter, which means that 1 cm is equal to 10 mm.

## Length Conversion

 kilometer (km) miles (mi) meter (m) feet (ft) centimeter (cm) inches (in) inches (in) centimeter (cm) yards (yd) meters (m) miles (m) kilometers (km)

5.1.4 Alternate Units of Measurement—the Système Internationale

5.1.6 Working with a Common Unit