Other Sizes

There have been many standard sizes of paper at different times and in different countries, but today there are two major systems in use: the international standard (A4 and its siblings), and the North American sizes. more...

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The international standard: ISO 216

The international paper size standard, ISO 216, is based on the German DIN 476 standard for paper sizes. Using the metric system, the base format is a sheet of paper measuring 1 m² in area (A0 paper size). Successive paper sizes in the series A1, A2, A3, etc., are defined by halving the preceding paper size parallel to its shorter side. The most frequently used paper size is A4 (210 × 297 mm).

This standard has been adopted by all countries in the world except the United States and Canada. In Mexico, Colombia and the Philippines, despite the ISO standard having been officially adopted, the U.S. "letter" format is still in common use.

ISO paper sizes are all based on a single aspect ratio of the square root of two, or approximately 1:1.4142. The advantages of basing a paper size upon this ratio were already noted in 1786 by the German scientist Georg Lichtenberg (in a letter to Johann Beckmann): if a sheet with aspect ratio √2 is horizontally divided into two equal halves, then the halves will again have aspect ratio √2. In the beginning of the twentieth century, Dr Walter Porstmann turned Lichtenberg's idea into a proper system of different paper sizes. Porstmann's system was introduced as a DIN standard (DIN 476) in Germany in 1922, replacing a vast variety of other paper formats. Even today the paper sizes are called "DIN A4" in everyday use in Germany.

The DIN 476 standard spread quickly to other countries, and before the outbreak of World War II it had been adopted by the following countries:

Belgium (1924); Netherlands (1925); Norway (1926); Switzerland (1929); Sweden (1930); Soviet Union (1934); Hungary (1938); Italy (1939);

During the war it was adopted by Uruguay (1942), Argentina (1943) and Brazil (1943); and directly afterwards the standard continued to spread to other countries:

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, and today only the U.S. and Canada have not adopted the system.

The largest standard size, A0, has an area of 1 m². The length of the long side of the sheet in metres is the 4th root of 2—approximately 1.189 metres. The short side is the reciprocal of this number, approximately 0.841 metres. A1 is formed by cutting a piece of A0 into two equal area rectangles. Because of the choice of lengths, the aspect ratio is the same for A1 as for A0 (as it is for A2, A3, etc). This particular measurement system was chosen to allow folding of one standard size into another, which cannot be accomplished with traditional paper sizes.

Read more at Wikipedia.org