The American license plate standard refers to a specific shape and size of license plate. Though originally conceived in the United States, the standard is also commonly used in both Canada and Mexico. Various Asian and Oceanic nations also use plates shaped to the American standard.

Specifically, the American standard refers only to size: 300mm in width, 150mm in height (or approximately 12 inches wide by 6 inches high). It was conceived during the mid-1950s as a partnership between the American (United States) auto industry and a variety of state governments, as a way of standardizing how much space needed to be allocated for the license plate on new cars. Unlike most other countries, the United States federal government played very little role in determining the parameters of this standard.

Before the advent of the standard, state governments had been free to make plates any size they wanted as long as the numbers fit - this meant that plates could often be as wide as 14 or 15 inches depending on the number of digits or the size of the dies being used. This difference in size, besides sometimes being incompatible with a given vehicle's styling, also created problems in how the plate was fastened to the vehicle. This helps to explain why many older plates (before the 1950s) have bolt holes in a variety of locations. Often, this was still to difficult to reconcile with the bolt locations on the vehicle, leading to the vehicle owner using wire or twine to attach the plate instead.

Though there was no specific date of adoption, most states (and Canadian provinces, as well as the Mexican government) had converted to the de facto standard by about 1958 or so. Since plate issuance was still generally done on an annual basis during this time, most vehicles in North America carried standard-sized plates starting with their 1959 registrations.

Countries using the American standard

The following list includes only those countries that are currently using the American standard or a close variation of it (at least by size). Countries that have since switched to other standards (or that have evolved into something completely different) are not included.

Country name Date of adoption Current baseplate
Canada c. 1956 Varies by province
Mexico 1960 Varies by state
United States c. 1956 Varies by state

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