The metric system is one of the world's most popular measuring systems. It is used in most countries in the world, with the large exception of the United States. Even in the U.S., however, scientific measurements are expressed in terms of the metric system.

The metric system itself was developed in France in 1791. It took a few years to catch on and be approved by the French government in 1799. Those were the years of the Napoleonic Wars, and the government had other matters it considered more pressing.

The metric system was eventually approved for general use in France and then gradually spread to other countries. It nearly became the official measuring system of the U.S. as well. The United States, however, kept its allegiance to the old English measuring system, even when Britain embraced the metric system. Only two other countries in the world, Liberia and Myanmar, still embrace the "English" measuring system. Shipments to and from these countries that involve transferal of goods to and from countries that use the metric system involve a good deal of unit conversion.

The official name of the metric system is the System Internationale (SI) or the International System of Units. The SI, or metric system, is a decimal system with a base of 10, making it easier for calculations than the American system. In the metric system, weights are measured in grams, dimensions in meters, and volumes in liters. Prefixes denote how much of something is being described in the metric system. With few exceptions, these prefixes come from the Greek language. A kilogram is a thousand grams. In the same way, a milliliter is one thousandth of a liter.

Another common measurement is that of temperature. The metric system uses a Celsius scale to measure temperature, and the English system uses Fahrenheit. The freezing point of water measured in degrees Celsius is 0 degrees, whereas Fahrenheit says that water freezes at 32 degrees. The boiling point of water in Celsius is 100 degrees; in Fahrenheit, water boils at 212 degrees.