A4s

A4s refer to the A-series family of paper sizes defined by ISO 216, with A4 being the most common size. The term is used to describe sheets that share the standard A4 format among other sizes in the series, which range from A0 to A10. The A-series is designed so that each size is half the area of the previous one when cut along the longer side, making A4 the most frequently used size in everyday documents.

The sizes share a constant aspect ratio of 1:√2. An A4 sheet measures 210 by 297 millimeters. When an A4 sheet is cut in half along its longer side, the halves become A5; halving again yields A6, and so on. The area of A0 is defined as 1 square meter, and A4 is one-sixteenth of A0.

The standard originated in the German DIN 476 specification in 1922 and was adopted internationally as ISO 216 in 1975. A-series sizes are widely used across Europe, Asia, Africa, and many other regions. In North America, Letter size is more common, but A4 is widely used for international documents and in offices with global operations.

A4s are used for everyday documents, letters, forms, and notebooks. They are common in printers, copiers, and scanners, and are compatible with a range of envelopes and packaging options (for example, C4 envelopes and DL envelopes are designed for folded A4 sheets). The uniform proportions across the A-series facilitate scaling, filing, and international document exchange.