Paper size standards govern the size of sheets of paper used as writing paper, stationery, cards, and for some printed documents. Most countries adhere to the ISO 216 standard, which includes the widely recognized A series (including A4 paper), defined by a consistent aspect ratio of √2. The system, first proposed in the 18th century and formalized in 1975, allows scaling between sizes without distortion. Regional variations exist, such as the North American paper sizes (e.g., Letter, Legal, and Ledger) which are governed by the ANSI and are used in North America and parts of Central and South America.
The standardization of paper sizes emerged from practical needs for efficiency. The ISO 216 system originated as DIN 476, later adopted internationally for its mathematical precision. The origins of North American sizes are lost in tradition and not well documented, although the Letter size () became dominant in the US and Canada due to historical trade practices in the 20th century. Other historical systems, such as the British Foolscap and Imperial sizes, have largely been phased out in favour of ISO or ANSI standards.
Regional preferences reflect cultural and industrial legacies. In addition to ISO and ANSI standards, Japan uses its JIS P 0138 system, which closely aligns with ISO 216 but includes unique B-series variants commonly used for books and posters. Specialized industries also employ non-standard sizes: newspapers use custom formats like Berliner and broadsheet, while envelopes and business cards follow distinct sizing conventions. The international standard for envelopes is the C series of ISO 269.
International standard paper sizes
The international paper size standard is ISO 216. It is based on the German DIN 476 standard for paper sizes. Each ISO paper size is one half of the area of the next larger size in the same series. ISO paper sizes are all based on a single aspect ratio of the square root of 2, or approximately 1:1.41421. There are different series, as well as several extensions.
The following international paper sizes are included in Cascading Style Sheets (CSS): A3, A4, A5, B4, B5.
A series
There are 11 sizes in the A series, designated A0–A10, all of which have an aspect ratio of , where is the long side and is the short side.
Since A series sizes share the same aspect ratio they can be scaled to other A series sizes without being distorted, and two sheets can be reduced to fit on exactly one sheet without any cutoff or margins.
The A0 base size is defined as having an area of 1 m; given an aspect ratio of , the dimensions of A0 are:
by .
or, rounded to the nearest millimetre, .
A series sizes are related in that the smaller dimension of a given size is the larger dimension of the next smaller size, and folding an A series sheet in half in its larger dimension—that is, folding it in half parallel to its short edge—results in two halves that are each the size of the next smaller A series size. As such, a folded brochure of a given A-series size can be made by folding sheets of the next larger size in half, e.g. A4 sheets can be folded to make an A5 brochure. The aspect ratio that allows this can be derived as follows:
The advantages of basing a paper size upon an aspect ratio of were noted in 1786 by the German scientist and philosopher Georg Christoph Lichtenberg. He also observed that some raw sizes already adhered to that ratio so that when a sheet is folded, the length to width ratio does not change.
Briefly after the introduction of the metric system, a handful of new paper formats equivalent to modern ones were developed in France, having been published for judicial purposes in 1798 during the French Revolution:
(A2) (A3) (B3) (B4) (B5) (B6)
These were never widely adopted, however.
Early in the 20th century, the ratio was used to specify the world format starting with as the short edge of the smallest size. Walter Porstmann started with the largest sizes instead, assigning one an area of (A0) and the other a short edge of (B0). He thereby turned the forgotten French sizes (relatively few in number) into a logically-simple and comprehensive plan for a full range of paper sizes, while introducing systematic alphanumeric monikers for them. Generalized to nothing less than four series, this 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 and Austria.
The DIN 476 standard spread quickly to other countries. Before the outbreak of World War II, it had been adopted by the following countries in Europe:
Belgium (1924) Netherlands (1925) Norway (1926) Finland (1927) Switzerland (1929) Sweden (1930) with later extensions Soviet Union (1934) with custom extensions Hungary (1938) Italy (1939)
During World War II, the standard spread to South America and was adopted by Uruguay (1942), Argentina (1943) and Brazil (1943), and afterwards spread to other countries:
Australia (1974) Austria (1948) Bangladesh (1972) Barbados (1973) Chile (1968) Colombia (1975) Czechoslovakia (1953) Denmark (1953) Ecuador (1974) France (1967) Greece (1970) Iceland (1964) India (1957) with custom extensions Iran (1948) Ireland (1959) Israel (1954) Japan (1951) with different B series Kuwait (1975) Mexico (1965) New Zealand (1963) Peru (1967) Poland (1957) Portugal (1954) Rhodesia (1970) Romania (1949) Singapore (1970) South Africa (1966) Spain (1947) Thailand (1973) Turkey (1967) United Kingdom (1971) Venezuela (1962) Yugoslavia(1956)
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.
The weight of an A-series sheet of a given paper weight can be calculated by knowing the ratio of its size to the A0 sheet. For example, an A4 sheet is the size of an A0 sheet, so if it is made from paper, it weighs of , which is .
B series
The B series paper sizes are less common than the A series. They have the same aspect ratio as the A series:
However, they have a different area. The area of B series sheets is in fact the geometric mean of successive A series sheets. B1 is between A0 and A1 in size, with an area of m, or about . As a result, B0 is 1 metre wide, and other sizes of the series are a half, a quarter, or further fractions of a metre wide: in general, every B size has exactly one side of length for . That side is the short side for B0, B2, B4, etc., and the long side for B1, B3, B5, etc.
While less common in office use, the B series is used for a variety of applications in which one A-series size would be too small but the next A-series size is too large, or because they are convenient for a particular purpose.
B4, B5, and B6 are used for envelopes that will hold C-series envelopes. B4 is quite common in printed music sheets. B5 is a relatively common choice for books. B7 is equal to the passport size ID-3 from ISO/IEC 7810. Many posters use B-series paper or a close approximation, such as 50 cm × 70 cm ~ B2.
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.
C series
The C series is defined in ISO 269, which was withdrawn in 2009 without a replacement, but is still specified in several national standards. It is primarily used for envelopes. 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 paper and C4 envelopes fit inside a B4 envelope.
Some envelope formats with mixed sides from adjacent sizes (and thus an approximate aspect ratio of 2:1) are also defined in national adaptations of the ISO standard, e.g. DIN C6/C5 (also known as C65) is 114 mm × 229 mm where the common side to C5 and C6 is 162 mm. This format allows an envelope holding an A-sized paper folded in three, e.g. for the C65, an A4.
Overview of ISO paper sizes + ISO paper sizes in portrait view (with rounded inch values) Format A series B series C series Size short × long Notional area short × long Notional area short × long Notional area mm in m mm in m mm in m 0 841 × 1189 2 = 1 1000 × 1414 2 ≈ 917 × 1297 2 ≈ 1 594 × 841 2 = 0.5 707 × 1000 2 ≈ 648 × 917 2 ≈ 2 420 × 594 2 = 0.25 500 × 707 2 ≈ 458 × 648 2 ≈ 3 297 × 420 2 = 0.125 353 × 500 2 ≈ 324 × 458 2 ≈ 4 210 × 297 2 = 0.0625 250 × 353 2 ≈ 229 × 324 2 ≈ 5 148 × 210 2 ≈ 176 × 250 2 ≈ 162 × 229 2 ≈ 6 105 × 148 2 ≈ 125 × 176 2 ≈ 114 × 162 2 ≈ 7 74 × 105 2 ≈ 88 × 125 2 ≈ 81 × 114 2 ≈ 8 52 × 74 2 ≈ 62 × 88 2 ≈ 57 × 81 2 ≈ 9 37 × 52 2 ≈ 44 × 62 2 ≈ 40 × 57 2 ≈ 10 26 × 37 2 ≈ 31 × 44 2 ≈ 28 × 40 2 ≈ i where where where
The variables are the distinct first terms in the three geometric progressions of the same common ratio equal to the square root of two. Each of the three geometric progressions (corresponding to the three series A, B, and C) is formed by all possible paper dimensions (length and width) of the series arranged in decreasing order. This arrangement of dimensions is also useful—not only does it form a geometric progression with easy-to-remember formulae, but also each consecutive pair of values (like a sliding window of size 2) will automatically correspond to the dimensions of a standard paper format in the series.
The tolerances specified in the standard are
± for dimensions up to , ± for lengths in the range and ± for any dimension above .
Related regional sizes
German original
The German standard DIN 476 was published on 18 August 1922 and is the original specification of the A, B and C sizes. In 1991, it was split into DIN 476-1 for the A and B formats and 476-2 for the C series. The former has been withdrawn in 2002 in favour of adopting the international standard as DIN EN ISO 216, but part 2 has been retained and was last updated in 2008.
The first and the second editions of DIN 476 from 1922 and 1925 also included a D series.
+ DIN D series paper sizes in portrait view (with rounded inch values) Format D series Size mm × mm inch × inch 0 1 2 3 4 5 6 7 8
The smallest formats in the original specifications for each series were A13, B13, C8, and D8. Sizes A11 through A13 were no longer listed in the 1930 edition, nor were B11 through B13. C9 and C10 were added in the 1976 revision for compatibility with photography sizes: C8 closely matches 6×9 photos, and C9 and C10 closely match 7×7 and 5×5 slides, respectively.
+ DIN 476:1922 tiny formats (with rounded inch values) Format A B Size mm × mm inch × inch mm × mm inch × inch 11 12 13
DIN 476 provides for formats larger than A0, denoted by a prefix factor. In particular, it lists the formats 2A0 and 4A0, which are twice and four times the size of A0 respectively. However, ISO 216:2007 notes 2A0 and 4A0 in the table of Main series of trimmed sizes (ISO A series) as well: "The rarely used sizes [2A0 and 4A0] which follow also belong to this series."
+ DIN 476 overformats (with rounded inch values) Name mm × mm inch × inch 4A0 2A0
DIN 476 also used to specify slightly tighter tolerances than ISO 216:
± for dimensions up to , ± for lengths in the range and