## What you’ll learn to do: Convert measurements between metric units and U.S. customary units

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 powers of 10. For example, a liter is 10 times larger than a deciliter, and a centigram is 10 times larger than a milligram. The metric system, with its decimal-based units, allows for easier unit conversions than the U.S. customary system, in which we have such unit ratios as 12 inches in a foot, 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 using powers of 10 is a good start.

In this section we will discover the basic units used in the metric system, and show how to convert between them. We will also explore temperature scales. In the United States, temperatures are usually measured using the **Fahrenheit** scale, while most countries that use the metric system use the **Celsius** scale to record temperatures. Learning about the different scales, including how to convert between them, will help you figure out what the weather is going to be like, no matter which country you find yourself in.