A0 size is a standard paper dimension defined by the ISO 216 international standard. It measures 841 millimeters in width and 1189 millimeters in height, making it one of the largest sizes in the A series. A0 is often used for posters, architectural drawings, and large-format prints. The A0 size is part of a series where each subsequent size is half the area of the previous one when folded in half parallel to its shorter sides. For example, A1 is half the size of A0, measuring 594 mm by 841 mm. This system allows for easy scaling of documents.