A4 Writing Paper
There are different series, as well as several extensions.
The following international paper sizes are included in Cascading Style Sheets (CSS): A3, A4, A5, B4, B5. Rounded to the nearest millimetre, that is 841 by 1,189 millimetres (33.1 in × 46.8 in).
The former has been withdrawn in 2002 in favor of adopting the international standard as DIN EN ISO 216, but part 2 has been retained and was last updated in 2008.
Some envelope formats with mixed sides from adjacent sizes (and thus an approximate aspect ratio of 2:1) are also defined in national adaptations of the ISO standard, e.g.
DIN C6/C5 is 114 mm × 229 mm where the common side to C5 and C6 is 162 mm.
Folded brochures of any size can be made by using sheets of the next larger size, e.g. The system allows scaling without compromising the aspect ratio from one size to another—as provided by office photocopiers, e.g. Similarly, two sheets of A4 can be scaled down and fit exactly on one sheet without any cutoff or margins.
The behavior of the aspect ratio is easily proven: on a sheet of paper, let a be the long side and b be the short side: Early in the 20th century, Dr Walter Porstmann turned Lichtenberg's idea into a proper system of different paper sizes.