A4 is a standard paper size, defined by the international standard ISO 216 as 210×297 mm (roughly 8.27×11.69 in). It is the normal size of paper for both domestic and business purposes in all countries except the United States, Mexico and Canada.

The aspect ratio of all international standard paper sizes is defined as the square root of two, before rounding, which ensures that if the paper is folded or cut in half, the halves maintain the aspect ratio, and are the next standard size down (A4 becomes two sheets of A5):

<math>\frac{297}{210} \approx \sqrt{2} \approx 1.4142<math>

See also

• Paper sizes

External link

• A thorough explanation of ISO paper sizes (http://www.cl.cam.ac.uk/~mgk25/iso-paper.html)

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