What is A4?

A3 is a standard paper size that’s part of the ISO 216 standard. It measures 210mm by 297mm or about 8.27 inches by 11.7 inches. A4 is part of the A series of paper sizes, with A0 being the largest and each subsequent size (A1, A2, A3, A4, etc) being half the size of the previous one when folded parallel to its shorter sides.

A4 is widely used in countries outside North America for letters, forms, and printing. In the US and Canada, the standard letter size is 8.5 inches by 11 inches (a bit wider but shorter). In North America, the sizes are part of a different system known as the ANSI/ASME Y14.1 standard.