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 these units.
The official name for this way of measuring things is the System Internationale (SI) or the International System of Units. SI is a decimal system with a base of 10, making it easier for calculations than the American system. Weights are measured in grams, dimensions in meters, and volumes in liters. Prefixes denote how much of something is being described, and with few exceptions, these prefixes come from the Greek language. A kilogram is 1,000 grams, for example, while a milliliter is 0.001 of a liter.
Another common measurement is that of temperature. The metric system uses a Celsius scale to measure temperature, while the English system uses Fahrenheit. Like all other measurements, temperatures are decimalized: the freezing point of water measured in degrees Celsius is 0° (32°F) and the boiling point is 100°C (212°F).
This system of measurement was developed in France in 1791, and it was approved by the French government in 1799. Those were the years of the Napoleonic Wars, and it took a few years because the government had other matters it considered more pressing. The system then gradually spread to other countries, and 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.