A3 is a commonly used standard of paper. The ISO 216 standard defines A3 size to be 297mm × 420mm, which is exactly double the size of an A4.
A3 sized paper is frequently used for office photocopying and printing, posters, folded brochures, advertisements, catalogues and more.
A3 paper size is quite versatile as it can be used as a small poster or folded once to create a four page A4 document or can be folded twice more to create a finished size of one third A4, leaving a six page brochure.
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.
- A3 is twice the size of A4.
- A3 is four times the size of A5 and eight times the size of A6.
- A3 is half the size of A2, and one quarter the size of A1.
- A3 is one-eighth the size of A0.