ISO 216 is the international standard by which paper sizes are determined. The system establishes three sets of paper sizes, known as the “A”, “B” and “C” series.
A4 is familiar to most as the most commonly available paper size in the world. A5 covers half the area of A4, A6 is half the area of A5 and so on. Conversely, A3 is double the area of A4, and so on up to A0, the largest in the series at 840 x 1188mm.