A2 is a paper size that is often used for medium size posters, architectural drawings, and diagrams.
A2 measures 420 × 594 millimeters or 16.54 × 23.39 inches. In PostScript, its dimensions are rounded off to 1190 × 1684 points.
Part of the ISO 216 standard
A2 is part of a set or range of page sizes, called the ISO A or ISO 216 standard. This international standard is based on the German DIN 476 standard from 1922. A5 is actually often referred to as DIN A5. The Japanese have adopted the same range of paper sizes in their JIS P 0138-61 standard.
By folding an A2 in two along its shortest side, you create an A3 document. Two A2 pages next to each other in a spread equals the A1 paper size. This way a range of paper sizes are created from A0 (which has a surface of one square meter) to A10. The height/width ratio remains constant (1:1.41 or the square root of 2) for all sizes. The dimensions always get rounded to the nearest millimeter.
Resolution needed to print an A2 size picture
To output an image properly it needs to have a certain minimum resolution. The number of pixels depends on the required output quality.
- At 300 ppi (pixels per inch) the image needs to be 4960 x 7016 pixels. This is the required resolution for quality offset printing that will be viewed from a short distance (such as books, brochures, magazines, calendars,…). For photos, it is also the optimum resolution but a somewhat lower pixel count (200 to 220 dpi) is acceptable for great-looking photographs.
- At 150 ppi the image needs to be 2480 x 3508 pixels. This is the minimum resolution for newspapers or posters viewed from a fairly short distance.
A digital camera with decent image quality and a resolution of 16 megapixels or more can be used to print high-quality A2 size pictures. Since such posters are usually viewed from a somewhat larger distance a 12-megapixel camera will still offer excellent quality and 8 megapixels will be considered good by many.
In the American market ISO paper sizes are hardly used at all. The US-alternative to A2 is called ANSI C and measures 17 × 22″ or 432 × 559 mm.
A bit of history
The dimensions of an A2 sheet actually go back to 1798 when the French government introduced the ‘grand registre’ paper size. It was meant to promote their newly established metric system. The idea of using a 1.414 aspect ratio was borrowed from Georg Lichtenberg, a German professor. In the early twentieth century, the Germans reused that concept to establish their DIN 476 standard.
Other sources of information
An elaborate yet easy to read page on the ISO 216 standard can be found here.