Letter size refers to a standard paper size commonly used in the United States and Canada, measuring 8.5 inches by 11 inches (21.6 cm by 27.9 cm). It is widely used for printing documents, letters, and forms in both personal and professional settings. This size is part of the ANSI paper size system, which includes other dimensions like Legal (8.5 x 14 inches) and Tabloid (11 x 17 inches). The letter size is favored for its convenience and compatibility with most printers and office equipment.