A marathon has an official distance of 42,195 meters (42.195 km), which is 26.219 miles (a.k.a. 26 miles, 385 yards). The approximation commonly seen on car stickers in the U.S., 26.2 [miles], is 33 yards too short. The three significant digit approximation in metric units: 42.2 [km] is 5 meters too long.
The distance is rooted in a Greek legend from the historic era.