km is the abbreviation for kilometer, a unit of length in the metric system. One kilometer equals 1,000 meters, or about 0.62 miles.

Most countries around the world use kilometers to measure long distances. Road signs in Canada, Europe, and Asia show distances in km. A 5 km race is a popular running distance, equal to about 3.1 miles. Scientists use kilometers when measuring things like the distance between cities, the depth of the ocean, or how far a spacecraft travels.

The United States is one of the few countries that primarily uses miles instead of kilometers for everyday measurements, though American scientists use km in their work. If you see a speed limit sign showing 100 in Canada, that means 100 km per hour, which is roughly 62 miles per hour. Understanding kilometers helps when you're traveling internationally, reading global news, or working on science projects that use the metric system.