One of the strengths of the metric system is that it has only one unit for each type of measurement. Other units are defined as simple products or quotients of these base units.
For example, the base unit for length (or distance) is the meter (m). Other units for length are described in terms of their relationship to a meter: A kilometer (km) is 1,000 m; a centimeter (cm) is 0.01 of a meter; and a millimeter (mm) is 0.001 of a meter.
Prefixes in the metric system are short names or letter symbols for numbers that are attached to the front of the base unit as a multiplying factor. A unit with a prefix attached is called a multiple of the unit -- it is not a separate unit. For example, just as you would not consider 1,000 in. a different unit from inches, a kilometer, which means 1,000 m, is not a different unit from meters.
Use the following Interactive Activity to explore some common units and prefixes in the metric system. Try to estimate the sizes of these objects in metric units before you start the activity, and pay attention to the patterns that emerge as you change prefixes:
This activity requires the Flash plug-in, which you can download for free from Macromedia's Web site. A non-interactive version of this activity is also available.