The official marathon distance is 26.2 miles, rounded to one decimal place.
The exact distance is 42.195 kilometers, or 26 miles and 385 yards. The measurement became standardized after the 1908 Olympic marathon in London, whose course ran from Windsor Castle to the royal box at the Olympic Stadium in Shepherd’s Bush.
Earlier Olympic and road marathons used varying distances. The 1908 route was later adopted as the standard by the International Amateur Athletic Federation, now known as World Athletics. A marathon is therefore longer than 26 miles by 385 yards, even though everyday descriptions usually say “26.2 miles.”
The distance is different from a half marathon, which is 21.0975 kilometers, or about 13.1 miles. It is also separate from ultramarathons, a broad category covering races longer than the standard marathon distance.