This depends on what kind of track you are running on. A standard running track is 400 meters long. A mile is 1600 meters, so four laps around a track will equate to one mile. However, it is important to understand how to calculate your mileage based on which lane you run in. The width of a typical track is divided into eight lanes. In track races, runners start in their own lanes, on their own starting blocks. Keep in mind that running a full circle on the outside lane of a track will actually be longer than running a full circle on the inside. A standard track that is 400 meters long means that it is actually the interior most lane, lane number 1, that is 400 meters in length. The farther out from the first lane you go, the longer your distance will become. So if you really want to make sure you are calculating your mileage, just stick to the interior lane.
However, not all tracks are created equal. What I mean by that is that not every single track around the world is the same distance. Some public parks, gyms, schools and colleges with an indoor or outdoor fitness center, and other public fitness places have oval tracks in which six, eight, ten, or another number of laps actually equals one mile. Like a standard 400-meter track, these tracks mean that a mile is equal to that number of laps when ran or walked on the inside lane. Most of these tracks will have a sign or marker that indicates how many laps equals a mile.
And a couple of things to consider if you are running on a track, 400 meters or otherwise. Run counterclockwise around the track. This is the direction that most runners run, and you should run with the "flow of traffic," not against it. Also, plan your workouts around the track's open hours, especially if it is a track that is used by a professional or school track team who use it during a scheduled practice time. Happy running!