In 1956, the U.S. states and Canadian provinces came to an agreement with the American Association of Motor Vehicle Administrators, the Automobile Manufacturers Association and the National Safety Council that standardized the size for license plates for vehicles (except those for motorcycles) at 6 inches (15 cm) in height by 12 inches (30 cm) in width, with standardized mounting holes, which has been the standard size for North American license plates since.
^Fox, Jams K. (1997). License Plates of the United States: A Pictorial History 1903-To the Present. Jerico, New York: Interstate Directory Publishing Company. ISBN9781886777002.
^Minard, Jeff; Stentiford, Tim (2004). A Moving History, 50 Years Of ALPCA. 100 Years Of License Plates. Paducah, Kentucky: Turner Publishing Company. p. 58. ISBN1-56311-975-7.