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A road sign written in Finnish that reads Joutsenlampi 0,5; Tornikahavila 1,5.
Figure 9.1 A road sign in Finland, a country that uses the metric system. (credit: modification of work by Anna Järvenpää/Flickr, Public Domain)

You are planning a road trip from your home state to the sunny beaches of Mexico and need to prepare a budget. While in the United States, gasoline is sold in gallons and distances are measured in miles, but in almost any other country you will find that gasoline is sold in liters and distance is measured in kilometers.

Whether you’re traveling, baking, watching an international sporting event, working with machine tools, or using scientific equipment, it's important to understand the metric system, or the International System of Units (SI). The metric system is a decimal measuring system that uses meters, liters, and grams to quantify length, capacity, and mass. It is used in all but three countries in the world, including the United States.

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