Many people associate notations such as 'A4', 'A3', 'B1', and 'B2' when they hear 'paper size'. This notation used for the size of copy paper and notebooks is defined by the international standard ISO ...
The default document size in Microsoft Word is 8.5-by-11 inches -- regular letter paper. However, the paper size for any document can be changed, whether it's an existing document or a new document.
The common letter-sized paper used in Europe and in most locations outside of North America. At 8.3 x 11.7" (210x297mm), A4 paper is slightly narrower and a little longer than "A" size 8.5 x 11" paper ...