The main advantage of this system is its scaling. Rectangular paper with an aspect ratio of √2 has the unique property that, when cut or folded in half midway between its longer sides, each half has the same √2 aspect ratio as the whole sheet before it was divided. Equivalently, if one lays two same-sized sheets of paper with an aspect ratio of √2 side by side along their longer side, they form a larger rectangle with the aspect ratio of √2 and double the area of each individual sheet.

Paper in the A series format has an aspect ratio of √2 (≈ 1.414, when rounded). A0 is defined so that it has an area of 1 m2 (11 sq ft) before rounding to the nearest 1 millimetre (0.039 in).