The Metric System
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134.5.1 The Metric System
Learning Objective(s)
1
Describe the general relationship between the U.S. customary units and metric units
of length, weight/mass, and volume.
2
Define the metric prefixes and use them to perform basic conversions among metric
units.
1
Objective
Introduction
In the United States, both the U.S. customary measurement system and the metric
system are used, especially in medical, scientific, and technical fields. In most other
countries, the metric system is the primary system of measurement. If you travel to other
countries, you will see that road signs list distances in kilometers and milk is sold in
liters. People in many countries use words like “kilometer,” “liter,” and “milligram” to
measure the length, volume, and weight of different objects. These measurement units
are part of the metric system.
Unlike the U.S. customary system of measurement, the metric system is based on 10s.
For example, a liter is 10 times larger than a deciliter, and a centigram is 10 times larger
than a milligram. This idea of “10” is not present in the U.S. customary system—there
are 12 inches in a foot, and 3 feet in a yard…and 5,280 feet in a mile!
So, what if you have to find out how many milligrams are in a decigram? Or, what if you
want to convert meters to kilometers? Understanding how the metric system works is a
good start.
What is Metric?
The metric system uses units such as meter, liter, and gram to measure length, liquid
volume, and mass, just as the U.S. customary system uses feet, quarts, and ounces to
measure these.
In addition to the difference in the basic units, the metric system is based on 10s, and
different measures for length include kilometer, meter, decimeter, centimeter, and
millimeter. Notice that the word “meter” is part of all of these units.
The metric system also applies the idea that units within the system get larger or smaller
by a power of 10. This means that a meter is 100 times larger than a centimeter, and a
kilogram is 1,000 times heavier than a gram. You will explore this idea a bit later. For
now, notice how this idea of “getting bigger or smaller by 10” is very different than the
relationship between units in the U.S. customary system, where 3 feet equals 1 yard,
and 16 ounces equals 1 pound.
Length, Mass, and Volume
The table below shows the basic units of the metric system. Note that the names of all
metric units follow from these three basic units.
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