a0

A0 is the largest size in the ISO 216 A-series of paper sizes. It is defined to have an area of exactly 1 square meter and an aspect ratio of 1:√2, a combination chosen to ensure that every successive size is half the area of the previous one when cut parallel to the shorter side. This design allows simple scaling for printing, copying, and storage.

The standard dimensions of A0 are 841 millimeters by 1189 millimeters. When A0 is cut in half along its longer side, it yields two sheets with the dimensions of A1; continuing the halving process produces A2, A3, and so on. This systematic sequence makes the A-series widely compatible with printers, scanners, and archival practices, particularly for technical drawings, posters, and large-format documents.

Origin and adoption: The DIN 476 standard established the A-series in Germany in the 1920s under Walter Porstmann and was later adopted internationally as ISO 216 in 1975. The naming convention uses uppercase letters (A0, A1, A2, etc.), with A0 representing the reference size from which the others derive.

Usage and regional context: The A-series is the predominant international standard for paper sizes outside of North America, where formats such as Letter and Legal are common. A0 and its descendants are frequently used for posters, architectural plans, drawings, and large-format printing, offering a consistent baseline for scaling documents across different devices and applications.