The ISO paper size A standard is based on each size being half of the size of the previous one, when folded parallel to the shorter lengths. This system allows for a variety of useful applications, such as the enlarging and reducing of images without any cutoff or margins, or folding to make a booklet of the next size down.

The diagrams below show the A page sizes in comparison to each other and with their sizes (click to open full-size).

A0 = 841 x 1189mm
A1 = 594 × 841mm
A2 = 420 × 594mm
A3 = 297 × 420mm
A4 = 210 × 297mm
A5 = 148 × 210mm
A6 = 105 x 148mm