a4

A4 is a standard paper size in the ISO 216 system, part of the A-series. It measures 210 by 297 millimeters (about 8.27 by 11.69 inches) and has an aspect ratio of 1:√2. This ratio is chosen so that every size in the series has the same proportions, and when the format is halved along its longer edge, the next size maintains the same shape. A0, the starting size, has an area of 1 square meter and dimensions 841 by 1189 millimeters; each subsequent size is obtained by halving the previous one. Therefore, A4 is the result of halving A3.

The A-series standard originated in Germany with the DIN 476 standard introduced in 1922 and was later formalized internationally as ISO 216 in 1975. The standardization aims to provide a convenient progression of sizes for documents and printing, with the A-family designed so that A4, A5, A6, and so on align across different applications.

A4 is the most widely used paper size outside North America, where other sizes such as Letter (8.5 by 11 inches) are more common. It is the typical default size for office printing, letterheads, forms, and everyday documents, and it is supported by virtually all printers, copiers, and scanners. In summary, A4’s precise dimensions, consistent aspect ratio, and global adoption have made it the de facto standard for everyday paper use in many parts of the world.