Letter size refers to a standard paper size commonly used in the United States and Canada. It measures 8.5 inches by 11 inches (21.6 cm by 27.9 cm) and is often used for printing documents, letters, and forms. This size is part of the larger family of paper sizes defined by the American National Standards Institute (ANSI). In contrast to A4 size, which is widely used in many other countries and measures 8.27 inches by 11.69 inches (21 cm by 29.7 cm), letter size is specifically designed for North American usage. Both sizes serve similar purposes but differ in dimensions, affecting how documents are formatted and printed.