II.

Using the Metric System

The metric system is known for its simplicity. All units of measurement in the metric system are based on decimals—that is, units that increase or decrease by multiples of ten. A series of Greek decimal prefixes is used to express units of ten or greater; a similar series of Latin decimal prefixes is used to express fractions. For example, deca equals ten, hecto equals one hundred, kilo equals one thousand, mega equals one million, giga equals one billion, and tera equals one trillion. For units below one, deci equals one-tenth, centi equals one-hundredth, milli equals one-thousandth, micro equals one-millionth, nano equals one-billionth, and pico equals one-trillionth. For conversion of metric system units to English-system units, see Weights and Measures.

The simplicity of the metric system is evident in how easily one unit of measure can be changed into another. To change units in the metric system, simply move the decimal point to the right or the left, depending on whether the unit of measurement is increasing or decreasing by ten or one hundred and so on. For example, 1,672,928 millimeters equals 167,292.8 centimeters, which equals 1,672.928 meters, which equals 1.672928 kilometers. Compare the ease of this conversion with English units by trying to convert 1,672,928 inches into feet, rods, furlongs, and miles.

A.

Length

People who were taught the English system of measurements in schools in the United States often have difficulty visualizing metric units. One way to visualize a meter is to think of the distance from the floor to the top of a doorknob, or the distance from the edge of an adult’s shoulder to the end of the opposite outstretched arm. Smaller things are measured in centimeters and millimeters. A millimeter is quite small, about the thickness of a dime. A centimeter is ten times bigger, about the height of a stack of ten dimes.

Millimeters are primarily used to measure very small items such as letters in a book, while centimeters are used to measure items ranging from the size of a book to the height of a person. Thereafter meters are used until one reaches distances about the length of five city blocks when kilometers are used. One kilometer is the approximate distance that an adult can walk in 12 minutes in a straight line and on a level road. Kilometers are used to measure long distances within cities or between cities.

B.

Volume

Small volumes, such as the contents of a drinking glass, are measured in cubic centimeters, and large volumes, such as the contents of industrial fuel tanks, are measured in liters. A liter is 1,000 cubic centimeters—also known as 1,000 milliliters. A normal-sized drinking glass contains about 300 milliliters. The size of a liter is increasingly well known in the United States because of the many one-liter beverage bottles found in grocery stores or supermarkets. Very large volumes are measured in cubic meters. Freight containers used in the shipping industry, including railroad, truck, and ocean shipping, have a capacity of about 70 cubic meters.

C.

Weight

The basic unit of weight in the metric system is called a gram, and it is equal to the weight of one cubic centimeter of water. This is a very small amount, but it is easy to comprehend. Just pick up a U.S. dollar bill (or any bank note), and its weight is one gram. Because the gram is too light to be a convenient standard of weight, a larger unit has been chosen. This unit is 1,000 grams. Following the regular pattern of metric naming, it is called one kilogram. One thousand grams of water occupy a volume of 1,000 cubic centimeters or one liter. So a person need only pick up a plastic one-liter bottle of water to understand how heavy a kilogram is. Very heavy objects are weighed in tons of 1,000 kilograms each. One thousand kilograms is equal to one metric ton and is not the same as the usual American ton of 907.2 kg.

Many other metric units exist, such as those for measuring area, pressure, and energy. However, these units are rarely encountered in everyday use.