In 1922, paper formats were specified in DIN 476. All formats have a page ratio of the page length to the diagonal length of a square.
DIN A0 corresponds to the approximate surface of 1 m², precisely 0.999949 m².
The A-series is primarily used for sheet and page formats. The format DIN A4 is one of the most frequently used formats (letterhead, books, leaflets, brochures).
The B-series is comprised of additional formats, of which B5 (176 x 250 mm) is a well-known and useful book format.
The C-series comprises the formats for covers and folders suitable for the A-series.