A0 is a less commonly used standard of paper due to its large size. The ISO 216 standard defines A0 size to be 841mm × 1189mm, which is also exactly double the size of an A1 and is also the largest size in the A series.
Usually A0 sized paper will be used for large format printing such as for posters and advertisements or graphics.
In the ISO paper size system, the height-to-width ratio of all pages is the square root of two. In other words, the width and the height of a page relate to each other like the side and the diagonal of a square. This aspect ratio is especially convenient for a paper size. If you put two such pages next to each other, or equivalently cut one parallel to its shorter side into two equal pieces, then the resulting page will have again the same width/height ratio.
- A0 is twice the size of A1, and four times the size of A2
- A0 is eight times the size of A3,
- A0 is sixteen times the size of A4, and thirty two times the size of A5.
- A0 is sixty four times the size of A6.