<Li> Kuwait (1975) </Li> <P> By 1975, so many countries were using the German system that it was established as an ISO standard, as well as the official United Nations document format . By 1977, A4 was the standard letter format in 88 of 148 countries . Today the standard has been adopted by all countries in the world except the United States and Canada . In Mexico, Costa Rica, Colombia, Venezuela, Chile, and the Philippines, the US letter format is still in common use, despite their official adoption of the ISO standard . </P> <P> In addition to the A series, there is a less common B series . The area of B series sheets is the geometric mean of successive A series sheets . So, B1 is between A0 and A1 in size, with an area of 0.707 m (​ ⁄ m). As a result, B0 is 1 metre wide, and other sizes in the B series are a half, a quarter or further fractions of a metre wide . While less common in office use, it is used for a variety of special situations . Many posters use B - series paper or a close approximation, such as 50 cm × 70 cm; B5 is a relatively common choice for books . The B series is also used for envelopes and passports . The B - series is widely used in the printing industry to describe both paper sizes and printing press sizes, including digital presses . B3 paper is used to print two US letter or A4 pages side by side using imposition; four pages would be printed on B2, eight on B1, etc . </P> <P> The C series is usually used for envelopes and is defined in ISO 269 . The area of C series sheets is the geometric mean of the areas of the A and B series sheets of the same number; for instance, the area of a C4 sheet is the geometric mean of the areas of an A4 sheet and a B4 sheet . This means that C4 is slightly larger than A4, and slightly smaller than B4 . The practical usage of this is that a letter written on A4 paper fits inside a C4 envelope, and both A4 and C4 paper fits inside a B4 envelope . </P>

What is the size of a typical poster