There are a number of paper sizing standards. The three series shown in the table below are the most commonplace for publishing and printing and are: ‘A’ sizes, ‘B’ sizes and ‘SRA’ sizes.
The international paper size standard, ISO 216, defines the ‘A’ sizes and is based on the German DIN 476 standard for paper sizes. ISO paper sizes are all based on a single aspect ratio of square root of 2, or approximately 1:1.4142. The base A0 size of paper is defined to have an area of one m². Rounded to millimetres the A0 paper size is 841 by 1,189 millimetres (33.1 × 46.8 in).