A3

A3 is a paper size that is typically used for drawings, diagrams and large tables. It is also frequently used in laser printers to output two A4 pages as a spread.

Dimensions

A3 measures 297 × 420 millimeters or 11.69 × 16.54 inches. In PostScript, its dimensions are rounded off to 842 × 1190 points.

Part of the ISO 216 standard

A3 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. A3 is actually often referred to as DIN A3. The Japanese have adopted the same range of paper sizes in their JIS P 0138-61 standard.
By folding an A3 in two along its shortest side, you create an A4 document. Two A3 pages next to each other in a spread equals the A2 paper size. This way a range of paper sizes is created from A0 (which has a surface of one square meter) to A10. The height/width ratio remains constant for all sizes: 1:1.41 or the square root of 2. The dimensions always get rounded to the nearest millimeter.

Alternatives

In the American market ISO paper sizes are hardly used at all. The US-alternative to A3 is called Tabloid or Ledger (ANSI B) and measures 11 x 17″ or 279 × 432 mm.

Other sources of information

An elaborate yet easy to read page on the ISO 216 standard can be found here.