Imperial Paper Sizes

Before adopting the international ISO 216 standard paper sizes, the United Kingdom historically used its own traditional British Imperial paper sizes which dated back centuries. The Imperial system included over 30 different large sheet sizes used for various purposes from Cartridge (21 x 26 inches) to huge formats like Grand Eagle (28.7 x 42 inches). The naming conventions derived from how these large sheets were folded - for example, 'Royal' paper is a 20 x 25 inch sheet which when folded three times makes 8 equal sheets called 'Royal Octavo' sheets at about 6.35 x 4 inches, a popular book size. So based on how these large master sheets were folded down into smaller pages for books or documents, the resulting page sizes were given names like quarto, octavo, and so on. While some former British territories continue using Imperial sizes for specific applications, globally the ISO A and B standard paper sizes (designed for easy scaling between sizes) have been widely adopted for international compatibility reasons. So the Imperial system persists mostly for legacy usage in select regions, while ISO formats dominate as the cross-border standards.