Paper size standards govern the size of sheets of paper used as writing paper, stationery, cards, and for some printed documents.

The ISO 216 standard, which includes the commonly used A4 size, is the international standard for paper size. It is used across the world except in North America and parts of Central and South America, where North American paper sizes such as "Letter" and "Legal" are used.^[1] 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.^[2]

A series

There are 11 sizes in the A series, designated A0–A10, all of which have an aspect ratio of ${\displaystyle {\frac {a}{b))={\sqrt {2))\approx 1.41421\ldots }$, where a is the long side and b is the short side.

Since A series sizes share the same aspect ratio ${\displaystyle ({\sqrt {2))),}$ 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 m²; given an aspect ratio of ${\displaystyle {\sqrt {2))}$, the dimensions of A0 are:

${\displaystyle {\sqrt[{4}]{2))\,\mathrm {m} }$ by ${\displaystyle {\frac {1}{\sqrt[{4}]{2))}\,\mathrm {m} }$.

or, rounded to the nearest millimetre, 1,189 mm × 841 mm (46.8 in × 33.1 in).

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 fact that halving a sheet with an aspect ratio of ${\displaystyle {\sqrt {2))}$ results in two sheets that themselves both have an aspect ratio of ${\displaystyle {\sqrt {2))}$ is proven as follows:

${\displaystyle {\frac {a}{b))={\sqrt {2)),}$

where a is the long side and b is the short side. The aspect ratio for the new dimensions of the folded paper is:

${\displaystyle {\frac {b}{\frac {a}{2))}=2{\frac {b}{a))=2{\frac {1}{\sqrt {2))}={\sqrt {2))={\frac {a}{b)).}$

The advantages of basing a paper size upon an aspect ratio of ${\displaystyle {\sqrt {2))}$ were noted in 1786 by the German scientist and philosopher Georg Christoph Lichtenberg.^[3] 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 proposed by the mathematician Lazare Carnot, and published for judicial purposes in 1798 during the French Revolution.^[4] These were never widely adopted, however:

• grand registre (A2)
• moyen papier (A3)
• grand papier (B3)
• petit papier (B4)
• demi feuille (B5)
• effets de commerce (half-B5)

Early in the 20th century, the ratio was used to specify the world format starting with 1 cm as the short edge of the smallest size. Walter Porstmann started with the largest sizes instead, assigning one an area of 1 m² (A0) and the other a short edge of 1 m (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" (IPA: [diːn.ʔaː.fiːɐ̯]) 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:

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:

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 1⁄16 the size of an A0 sheet, so if it is made from 80-g/m² paper, it weighs 1⁄16 of 80 g, which is 5 g.

B series

The B series paper sizes are less common than the A series. They have the same aspect ratio as the A series:

${\displaystyle {\frac {a}{b))={\sqrt {2))=1.41...}$

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 ${\displaystyle {\frac {1}{\sqrt {2))))$ m², or about 0.707 m². 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 ${\displaystyle {\frac {1\operatorname {m} }{2^{n))))$ for ${\displaystyle n\in \mathbb {N} }$. 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.^{[need quotation to verify]}

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 envelope fits 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[6]			B series[7]			C series[8]
Size	short × long		Notional area	short × long		Notional area	short × long		Notional area
	mm	in	m2	mm	in	m2	mm	in	m2
0	841 × 1189	33.1 × 46.8	20 = 1	1000 × 1414	39.4 × 55.7	21⁄2 ≈ 1.414	917 × 1297	36.1 × 51.1	21⁄4 ≈ 1.189
1	594 × 841	23.4 × 33.1	1/2 = 0.5	707 × 1000	27.8 × 39.4	2−1⁄2 ≈ 0.707	648 × 917	25.5 × 36.1	2−3⁄4 ≈ 0.595
2	420 × 594	16.5 × 23.4	1/22 = 0.25	500 × 707	19.7 × 27.8	2−1+1⁄2 ≈ 0.354	458 × 648	18.0 × 25.5	2−1+3⁄4 ≈ 0.297
3	297 × 420	11.7 × 16.5	1/23 = 0.125	353 × 500	13.9 × 19.7	2−2+1⁄2 ≈ 0.177	324 × 458	12.8 × 18.0	2−2+3⁄4 ≈ 0.149
4	210 × 297	8.3 × 11.7	1/24 = 0.0625	250 × 353	9.8 × 13.9	2−3+1⁄2 ≈ 0.088	229 × 324	9.0 × 12.8	2−3+3⁄4 ≈ 0.0743
5	148 × 210	5.8 × 8.3	1/25 ≈ 0.0313	176 × 250	6.9 × 9.8	2−4+1⁄2 ≈ 0.044	162 × 229	6.4 × 9.0	2−4+3⁄4 ≈ 0.0372
6	105 × 148	4.1 × 5.8	1/26 ≈ 0.0156	125 × 176	4.9 × 6.9	2−5+1⁄2 ≈ 0.0221	114 × 162	4.5 × 6.4	2−5+3⁄4 ≈ 0.0186
7	74 × 105	2.9 × 4.1	1/27 ≈ 0.0078	88 × 125	3.5 × 4.9	2−6+1⁄2 ≈ 0.0110	81 × 114	3.2 × 4.5	2−6+3⁄4 ≈ 0.0093
8	52 × 74	2.0 × 2.9	1/28 ≈ 0.0039	62 × 88	2.4 × 3.5	2−7+1⁄2 ≈ 0.0055	57 × 81	2.2 × 3.2	2−7+3⁄4 ≈ 0.0046
9	37 × 52	1.5 × 2.0	1/29 ≈ 0.0020	44 × 62	1.7 × 2.4	2−8+1⁄2 ≈ 0.0028	40 × 57	1.6 × 2.2	2−8+3⁄4 ≈ 0.0023
10	26 × 37	1.0 × 1.5	1/210 ≈ 0.00098	31 × 44	1.2 × 1.7	2−9+1⁄2 ≈ 0.0014	28 × 40	1.1 × 1.6	2−9+3⁄4 ≈ 0.0012
i	${\displaystyle \left(\alpha _{A}\cdot r^{i+1}\right)\times \left(\alpha _{A}\cdot r^{i}\right),}$ where ${\displaystyle \alpha _{A}={\sqrt[{4}]{2))\,{\text{m));r={\tfrac {1}{\sqrt {2))))$			${\displaystyle \left(\alpha _{B}\cdot r^{i+1}\right)\times \left(\alpha _{B}\cdot r^{i}\right),}$ where ${\displaystyle \alpha _{B}={\sqrt {2))\,{\text{m));r={\tfrac {1}{\sqrt {2))))$			${\displaystyle \left(\alpha _{C}\cdot r^{i+1}\right)\times \left(\alpha _{C}\cdot r^{i}\right),}$ where ${\displaystyle \alpha _{C}={\sqrt[{8}]{8))\,{\text{m));r={\tfrac {1}{\sqrt {2))))$

The ${\displaystyle \alpha }$ 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 interesting arrangement of dimensions is also very 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

• ±1.5 mm (0.06 in) for dimensions up to 150 mm (5.9 in),
• ±2 mm (0.08 in) for lengths in the range 150 to 600 mm (5.9 to 23.6 in) and
• ±3 mm (0.12 in) for any dimension above 600 mm (23.6 in).

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 favor 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.

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 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 also used to specify slightly tighter tolerances than ISO 216:

• ±1 mm (0.04 in) for dimensions up to 150 mm (5.9 in),
• ±1.5 mm (0.06 in) for lengths in the range 150 mm to 600 mm (5.9 to 23.6 in) and
• ±2 mm (0.08 in) for any dimension above 600 mm (23.6 in).

There used to be a standard, DIN 198, that was just a table of recommended A series formats for a number of business applications. The 1976 edition of this standard introduced a size 2⁄3 A4 198 mm × 210 mm and suggested it for some forms and slips.

Swedish extensions

The Swedish standard SIS 01 47 11^[9] generalized the ISO system of A, B, and C formats by adding D, E, F, and G formats to it. Its D format sits between a B format and the next larger A format (just like C sits between A and the next larger B). The remaining formats fit in between all these formats, such that the sequence of formats A4, E4, C4, G4, B4, F4, D4, *H4, A3 is a geometric progression, in which the dimensions grow by a factor ${\displaystyle {\sqrt[{16}]{2))}$ from one size to the next. However, this SIS standard does not define any size between a D format and the next larger A format (called *H in the previous example).

Of these additional formats, G5 (169 × 239 mm) and E5 (155 × 220 mm) are popular in Sweden and the Netherlands for printing dissertations,^[10] but the other formats have not turned out to be particularly useful in practice. They have not been adopted internationally and the Swedish standard has been withdrawn.

The Swedish and German D series basically contain the same sizes but are offset by one, i.e. DIN D4 equals SIS D5 and so on.

SIS 014711 formulas,^[11] including the missing step, series *H, between D and A,
${\textstyle n=0..10,r={\sqrt[{16}]{2)),s={\sqrt {\frac {1}{2))))$

Designation	Shorter edge	Longer edge
An	r−4 × sn	r+4 × sn
En	r−3 × sn	r+5 × sn
Cn	r−2 × sn	r+6 × sn
Gn	r−1 × sn	r+7 × sn
Bn	r 0 × sn	r+8 × sn
Fn	r+1 × sn	r+9 × sn
Dn	r+2 × sn	r+10 × sn
*Hn	r+3 × sn	r+11 × sn
A(n-1)	r+4 × sn	r+12 × sn

Japanese variation

The Japanese standard JIS P 0138 defines two main series of paper sizes. The JIS A-series is identical to the ISO A-series except that it has slightly different tolerances. The area of B-series paper is 1.5 times that of the corresponding A-paper (instead of the factor ${\displaystyle {\sqrt {2))=1.414...}$ for the ISO B-series), so the length ratio is approximately 1.22 times the length of the corresponding A-series paper. The aspect ratio of the paper is the same as for the A-series paper. Both A- and B-series paper are widely available in Japan, Taiwan and China, and most photocopiers are loaded with at least A4 and either one of A3, B4, and B5 paper.

Cascading Style Sheets (CSS) only supports the most popular of the Japanese sizes, JIS-B4 and JIS-B5.^[2]

A popular size for books, dubbed AB, combines the shorter edges of A4 and B4. Another two with an aspect ratio approximating 16:9 are 20% narrower variants of A6 and B6, respectively, the latter resulting from cutting JIS B1 into 4 × 10 sheets (thus "B40").

There are also a number of traditional paper sizes, which are now used mostly by printers. The most common of these old series is the Shiroku-ban and the Kiku paper sizes.

Chinese extensions

The Chinese standard GB/T 148–1997,^[12] which replaced GB 148–1989, documents the standard ISO series, A and B, but adds a custom D series. This Chinese format originates from the Republic of China (1912–1949). The D series is not identical to the German or Swedish D series. It does not strictly follow the same principles as ISO paper sizes: The aspect ratio is only very roughly ${\displaystyle {\sqrt {2))}$. The short side of the size is always 4 mm longer than the long side of the next smaller size. The long side of the size is always exactly – i.e. without further rounding – twice as long as the short side of the next smaller size.

Indian variants

The Bureau of Indian Standards recommends the "ISO-A series" size of drawing sheet for engineering drawing works. The Bureau of Indian Standards specifies all the recommendations for engineering drawing sheets in its bulletin IS 10711: 2001.^[13]

The Bureau extended the ISO-A series with a Special Elongated Sizes (Second Choice). These sizes are achieved by increasing the shorter dimensions of a sheet of the ISO A series to lengths that are multiples of the shorter dimensions of the chosen basic sheet; in effect, all of the Indian elongated sizes emulate having several regular-size sheets joined on their long edge.

There is also a Exceptional Elongated Sizes (Third Choice). These sizes are obtained by increasing the shorter dimensions of a sheet of the ISO-A series to lengths that are multiples of the shorter dimensions of the chosen basic sheet. These sizes are used when a very large or extra elongated sheet is needed.

Soviet variants

The first standard of paper size in the Soviet Union was OST 303 in 1926. Six years later, it was replaced by OST 5115 which generally followed DIN 476 principles, but used Cyrillic lowercase letters instead of Latin uppercase, had the second row shifted so that б₀ (B0) roughly corresponded to B1 and, more importantly, had slightly different sizes:^[14]

The general adaptation of ISO 216 in the Soviet Union, which replaced OST 5115, was GOST 9327. In its 1960 version, it lists formats down to A13, B12 and C8 and also specifies 1⁄2, 1⁄4 and 1⁄8 prefixes for halving the shorter side (repeatedly) for stripe formats, e.g. 1⁄2A4 = 105 mm × 297 mm.

A standard for technical drawings from 1960, GOST 3450,^[15] introduces alternative numeric format designations to deal with very high or very wide sheets. These 2-digit codes are based upon A4 = "11": The first digit is the factor the longer side (297 mm) is multiplied by and the second digit is the one for the shorter side (210 mm), so "24" is 2×297 mm × 4×210 mm = 594 mm × 840 mm.

GOST 3450 from 1960 was replaced by ESKD GOST 2301 in 1968,^[16] but the numeric designations remained in popular use much longer. The new designations were not purely numeric but consisted of the ISO label followed by an 'x', or possibly the multiplication sign '×', and the factor, e.g. DIN 2A0 = GOST A0×2, but DIN 4A0 ≠ GOST A0×4, also listed are: A0×3, A1×3, A1×4, A2×3–A2×5, A3×3–A3×7, A4×3–A4×9. The formats ...×1 and ...×2 usually would be aliases for existing formats.

Elongated sizes

ISO 5457, last updated in 1999,^[17] introduces elongated sizes that are formed by a combination of the dimensions of the short side of an A-size (e.g. A2) with the dimensions of the long side of another larger A-size (e.g. A0). The result is a new size, for example with the abbreviation A2.0 we would have a 420 × 1189 mm size.

These drawing paper sizes have been adopted by ANSI/ASME Y14.1M for use in the United States, alongside A0 through A4 and alongside inch-based sizes.

International envelope and insert sizes

DIN 5008 (previously DIN 676) prescribes, among many other things, two variants, A and B, for the location of the address field on the first page of a business letter and how to fold the A4 sheet accordingly, so the only part visible of the main content is the subject line.

International raw sizes

ISO 5457 specifies drawing paper sizes with a trimmed size equal to the A series sizes from A4 upward. The untrimmed sizes are 3 to 4 cm larger and rounded to the nearest centimeter. A0 through A3 are used in landscape orientation, while A4 is used in portrait orientation. Designations for preprinted drawing paper include the base sizes and a suffix, either T for trimmed or U for untrimmed sheets.

The withdrawn standard ISO 2784 did specify sizes of continuous, fan-fold forms based upon whole inches as was common for paper in continuous lengths in automatic data processing (ADP) equipment. Specifically, 12 inches (304.8 mm) were considered an untrimmed variant of the A4 height of 297 mm.

Transitional paper sizes

PA4 or L4

A transitional size called PA4 (210 mm × 280 mm or 8.27 in × 11.02 in), sometimes dubbed L4, was proposed for inclusion into the ISO 216 standard in 1975. It has the height of Canadian P4 paper (215 mm × 280 mm, about 8+1⁄2 in × 11 in) and the width of international A4 paper (210 mm × 297 mm or 8.27 in × 11.69 in), i.e. it uses the smaller value among the two for each side. The table shows how this format can be generalized into an entire format series.

The PA formats did not end up in ISO 216, because the committee decided that the set of standardized paper formats should be kept to the minimum necessary.^{[citation needed]} However, PA4 remains of practical use today. In landscape orientation, it has the same 4:3 aspect ratio as the displays of traditional TV sets, some computer displays (e.g. the iPad) and data projectors. PA4, with appropriate margins is, therefore, a good choice as the format of presentation slides.

As a compromise between the two most popular paper sizes globally, PA4 is used today by many international magazines, because it can be printed easily on equipment designed for either A4 or US Letter. That means (in practice) it has turned out to be not so much a paper size as a page format. Apple, for instance, requires this format for digital music album booklets.^[18]

The size 210 mm × 280 mm was documented in the Canadian standard CAN2-200.2-M79 "Common Image Area for Paper Sizes P4 and A4".^[19]

F4

A non-standard F4 paper size is common in Southeast Asia. It is a transitional size with the shorter side of ISO A4 (210 mm, 8+1⁄4 inch) and the longer side of British Foolscap (13-inch, 330 mm). ISO A4 is exactly 90% the height of F4. This size is sometimes also known as (metric) 'foolscap' or 'folio'.

In some countries, the narrow side of F4 is slightly broader: 8.5 inches (216 mm) or 215 mm. It is then equivalent to the US Government Legal and Foolscap Folio sizes. In Indonesia, where it is the legally-mandated paper size for use in the printing of national legislation, it is sometimes called Folio or HVS (from Dutch: houtvrij schrijfpapier, "wood-free writing paper"). In Philippines, it is commonly called long bond as opposed to short bond which refers to the US Letter paper size.

A sheet of F4 can be cut from a sheet of SRA4 with very little wastage. The size is also smaller than its Swedish equivalent SIS F4 at 239 mm × 338 mm.

Weltformat

The Weltformat (world format) was developed by German chemist Wilhelm Ostwald in 1911 as part of Die Brücke, around the same time DIN 476 was first discussed. It shares the same design primitives, especially the aspect ratio, but is based upon 1 cm as the short edge of the smallest size. Sizes were designated by roman numerals. The result, for the fourth through fourteenth size, is close to the DIN/ISO C series. ^[20]

^[21]

The sizes have been used for some print products in the early 20th century in central Europe but got replaced by DIN sizes almost entirely. However, it was successfully adopted from 1913 onwards for posters and placards in Switzerland. Even today, the default size for posters in Swiss advertisements, F4, is colloquially known as Weltformat, although it measures 895 mm × 1280 mm, i.e. 1 cm less than size XIV. ^[22] This poster size goes alongside F12 "Breitformat" 2685 mm × 1280 mm (3 × F4) and F24 "Großformat" 2685 mm × 2560 mm (2 × 3 × F4, ) as well as F200 "Cityformat" 1165 mm × 1700 mm.

A0a

Although the movement is towards the international standard metric paper sizes, on the way there from the traditional ones there has been at least one new size just a little larger than that used internationally.

British architects and industrial designers once used a size called "Antiquarian", 31 in × 53 in (787 mm × 1,346 mm), as listed above, but given in the New Metric Handbook (Tutt & Adler 1981) as 813 mm × 1,372 mm (32 in × 54 in) for board size. This is a little larger than ISO A0, 841 mm × 1189 mm. So for a short time, a size called A0a of 1,000 mm × 1,370 mm (39.4 in × 53.9 in) was used in Britain, which is actually just a slightly shorter version of ISO B0 at 1414 mm.

Pliego

The most common paper sizes used for commercial and industrial printing in Colombia are based upon a size referred to as pliego that is ISO B1 (707 mm × 1000 mm) cut to full decimetres. Smaller sizes are derived by halving as usual and just get a vulgar fraction prefix: 1⁄2 pliego and 1⁄4 pliego.

K

In East Asia, i.e. Japan, Taiwan, and China in particular, there is a number of similar paper sizes in common use for book-making and other purposes. Confusingly, a single designation is often used with slightly different edge measures: The base sheet is labeled 1K (or 1开, where K stands for Chinese: 开本; pinyin: kāiběn; lit. 'folio'; or 1切/1取 in Japanese); all smaller sizes derived by halving have the power of two number, i = 2ⁿ, in front of the uppercase letter K. The number in ISO designations, in contrast, is the exponent n that would yield the number of sheets cut from the base sizes.

The sizes of such folios depend on the base sheet. Pre-metric standards include:

• The imperial 菊判 (kiku-ban), named after the Chrysanthemum watermark on imperial paper, measuring 636mm × 939mm.
• The four-by-six 四六判 shi-roku-ban (4×6 or 4/6), where the final size at 32K was measured 4 by 6 sun in Japan, c. 121 × 181 mm, or slightly more, 127 or 130 × 188 mm i.e. 4.2 or 4.3 × 6.2 sun.
  • In Taiwan, the traditional base size 1K inherited from Japan is sometimes quoted as measuring 31 × 43 inches exactly, which is off by c. 1 millimeter from the commonly quoted metric base size of 788 × 1091 mm, which is directly derived from 26 × 36 sun or 2.6 × 3.6 shaku.
• The three-by-five 三五判 (3×5 or 3/5), where the final size at 32K is slightly less than 3 by 5 sun, often given as 84 × 148 mm which would be c. 2.8 × 4.9 sun.

The 4/6 standard has given rise to newer metric book-size standards, including:

• The modern Japanese size for books, simply labeled B and is specified as 765 × 1085 millimeters. It is not directly related to the similar JIS B series, where B1 is slightly smaller.
• The Chinese SAC D series.

North American paper sizes

Inch-based loose sizes

The United States, Canada, and the Philippines^[1] primarily use a different system of paper sizes from the rest of the world. The current standard sizes are unique to those countries, although due to the size of the North American market and proliferation of both software and printing hardware from the region, other parts of the world have become increasingly familiar with these sizes (though not necessarily the paper itself). Some traditional North American inch-based sizes differ from the Imperial British sizes described below.

Common American loose sizes

Letter, Legal and Ledger/Tabloid are by far the most commonly used of these for everyday activities, and the only ones included in Cascading Style Sheets (CSS).

The origins of the exact dimensions of Letter size paper are lost in tradition and not well documented. The American Forest and Paper Association argues that the dimension originates from the days of manual papermaking and that the 11-inch length of the page is about a quarter of "the average maximum stretch of an experienced vatman's arms."^[27] However, this does not explain the width or aspect ratio.

Outside of North America, Letter size may also be known as "American Quarto".^[28] If one accepts some trimming, the size is indeed one quarter of the old Imperial paper size known as Demy, 17+1⁄2 in × 22+1⁄2 in (444 mm × 572 mm).^[29] Manufacturers of computer printers, however, recognize inch-based Quarto as 10+5⁄6 or 10.83 in (275 mm) long.^[24]

Usage and adoption

US paper sizes are currently standard in the United States and are the most commonly used formats at least in the Philippines, most of Mesoamerica^[30] and Chile. The latter use US Letter, but their Legal size is 13 inches tall (recognized as Foolscap by printer manufacturers,^[24] i.e. one inch shorter than its US equivalent.^[31]

Mexico and Colombia, for instance, have adopted the ISO standard, but the US Letter format is still the system in use throughout the country. It is rare to encounter ISO standard papers in day-to-day uses, with Carta (Letter), Oficio (Government-Legal), and Doble carta (Ledger/Tabloid) being nearly universal. Printer manufacturers, however, recognize Oficio as 13.4 in (340 mm) long.^[24]

In Canada, select US paper sizes are a de facto standard.

Variant American loose sizes

There is an additional paper size, 8 in × 10+1⁄2 in (205 mm × 265 mm), to which the name Government-Letter was given by the IEEE Printer Working Group (PWG).^[24] It was prescribed by Herbert Hoover when he was Secretary of Commerce to be used for US government forms, apparently to enable discounts from the purchase of paper for schools, but more likely due to the standard use of trimming books (after binding) and paper from the standard letter size paper to produce consistency and allow "bleed" printing. In later years, as photocopy machines proliferated, citizens wanted to make photocopies of the forms, but the machines did not generally have this size of paper in their bins. Ronald Reagan therefore had the US government switch to regular Letter size, which is half an inch both longer and wider.^[27] The former government size is still commonly used in spiral-bound notebooks, for children's writing and the like, a result of trimming from the current Letter dimensions.

By extension of the American standards, the halved Letter size, 5+1⁄2 in × 8+1⁄2 in (140 mm × 215 mm), meets the needs of many applications. It is variably known as Statement, Stationery, Memo, Half Letter, Half A (from ANSI sizes) or simply Half Size, and as Invoice by printer manufacturers.^[24] Like the similar-sized ISO A5, it is used for everything from personal letter writing to official aeronautical maps. Organizers, notepads, and diaries also often use this size of paper; thus 3-ring binders are also available in this size. Booklets of this size are created using word processing tools with landscape printing in two columns on letter paper which are then cut or folded into the final size.

A foot-long sheet with the common width of Letter and (Government) Legal, i.e. 8+1⁄2 in × 12 in (215 mm × 305 mm), would have an aspect ratio very close to the square root of two as used by international paper sizes and would actually almost exactly match ISO RA4 (215 mm × 305 mm). This size is sometimes known as European Fanfold.^[24]

While Executive refers to 7+1⁄4 in × 10+1⁄2 in (185 mm × 265 mm) in America, the Japanese organization for standardization specified it as 216 mm × 330 mm (8.5 in × 13.0 in), which is elsewhere known as Government Legal or Foolscap.

Standardized American paper sizes

In 1996, the American National Standards Institute adopted ANSI/ASME Y14.1 which defined a regular series of paper sizes based upon the de facto standard 8+1⁄2 in × 11 in (216 mm × 279 mm) Letter size which it assigned "ANSI A", intended for technical drawings, hence sometimes labeled "Engineering". This series is somewhat similar to the ISO standard in that cutting a sheet in half would produce two sheets of the next smaller size and therefore also includes Ledger/Tabloid^[25] as "ANSI B". Unlike the ISO standard, however, the arbitrary base sides forces this series to have two alternating aspect ratios. For example, ANSI A is less elongated than A4, while ANSI B is more elongated than A3.

The Canadian standard CAN2 9.60-M76 and its successor CAN/CGSB 9.60-94 "Paper Sizes for Correspondence" specified paper sizes P1 through P6, which are the U.S. paper sizes rounded to the nearest 5 mm.^[32] All custom Canadian paper size standards were withdrawn in 2012.^[33]

With care, documents can be prepared so that the text and images fit on either ANSI or their equivalent ISO sheets at a 1:1 reproduction scale.

Other, informal, larger sizes continuing the alphabetic series illustrated above exist, but they are not part of the series per se, because they do not exhibit the same aspect ratios. For example, Engineering F size is 28 in × 40 in or 711 mm × 1,016 mm with ca. 1.4286:1; it is commonly required for NAVFAC drawings, but is generally less commonly used. Engineering G size is 22+1⁄2 in (572 mm) high, but it is a roll format with a variable width up to 90 in (2.3 m) in increments of 8+1⁄2 in (216 mm). Engineering H through N sizes are also roll formats.

Such huge sheets were at one time used for full-scale layouts of aircraft parts, automotive parts, wiring harnesses, and the like, but are slowly being phased out, due to widespread use of computer-aided design (CAD) and computer-aided manufacturing (CAM). Some visual arts fields also continue to use these paper formats for large-scale printouts, such as for displaying digitally painted character renderings at life-size as references for makeup artists and costume designers or to provide an immersive landscape reference.

Architectural sizes

In addition to the system as listed above, there is a corresponding series of paper sizes used for architectural purposes defined in the same standard, ANSI/ASME Y14.1, which is usually abbreviated "Arch". This series also shares the property that bisecting each size produces two of the size below, with alternating aspect ratios. It may be preferred by North American architects because the aspect ratios (4:3 and 3:2) are ratios of small integers, unlike their ANSI (or ISO) counterparts. Furthermore, the aspect ratio 4:3 matches the traditional aspect ratio for computer displays.

The size Arch E1 has a different aspect ratio because it derives from adding 6 inches to each side of Arch D or subtracting the same amount from Arch E. Printer manufacturer recognize it as wide-format.^[24] An intermediate size between Arch C and D with a long side of 30 inches (760 mm) does not exist.

Demitab

The demitab or demi-tab (a portmanteau of the French word 'demi' [half] and 'tabloid') is 8 in × 10+1⁄2 in (203 mm × 267 mm), i.e. roughly one half of a sheet of 11 in × 17 in (279 mm × 432 mm) tabloid-size paper.^[35]

"Demitab", "broadsheet" or "tabloid" format newspapers are not necessarily printed on paper measuring exactly their nominal size.

Notebook sizes

The sizes listed above are for paper sold loose in reams. There are many sizes of tablets of paper, that is, sheets of paper bound at one edge, usually by a strip of plastic or hardened PVA adhesive. Often there is a pad of cardboard (also known as paperboard or greyboard) at the bottom of the stack. Such a tablet serves as a portable writing surface, and the sheets often have lines printed on them, usually in non-repro blue, to make writing in a line easier. An older means of binding is to have the sheets stapled to the cardboard along the top of the tablet; there is a line of perforated holes across every page just below the top edge from which any page may be torn off. Lastly, a pad of sheets each weakly stuck with adhesive to the sheet below, trademarked as "Post-It" or "Stick-Em" and available in various sizes, serve as a sort of tablet.

"Letter pads" are 8+1⁄2 in × 11 in (220 mm × 280 mm), while the term "legal pad" is often used by laymen to refer to pads of various sizes including those of 8+1⁄2 in × 14 in (220 mm × 360 mm). Stenographers use "steno pads" of 6 in × 9 in (150 mm × 230 mm). The steno pad size is also used by Scholastic Corporation as the textblock size of their hardcover editions of the Harry Potter novels, with paperback editions using DIN D6.

Envelope sizes

This implies that all postcards have an aspect ratio in the range from 20∶17 = 1.18 to 12∶7 = 1.71, but the machinable aspect ratio is further restricted to a minimum of 1.30. The only ISO 216 size in the US postcard range is A6. The theoretical maximum aspect ratio for enveloped letters is 23∶7 = 3.29, but is explicitly limited to 2.50.

Personal organizer sizes

Index card sizes

Photography sizes

Grain

Most industry standards express the direction of the grain last when giving dimensions (that is, 17 × 11 inches is short grain paper and 11 × 17 inches is long grain paper), although alternatively the grain alignment can be explicitly indicated with an underline (11 × 17 is a short grain) or the letter "M" for "machine" (11M × 17 is a short grain). Grain is important because the paper will crack if folded across the grain: for example, if a sheet 17 × 11 inches is to be folded to divide the sheet into two 8.5 × 11 halves, then the grain will be along the 11-inch side.^[39] Paper intended to be fed into a machine that will bend the paper around rollers, such as a printing press, photocopier or typewriter, should be fed grain edge first so that the axis of the rollers is along the grain.

Traditional inch-based paper sizes

Traditionally, a number of different sizes were defined for large sheets of paper, and paper sizes were defined by the sheet name and the number of times it had been folded. Thus a full sheet of "royal" paper was 25 × 20 inches, and "royal octavo" was this size folded three times, so as to make eight sheets, and was thus 10 × 6+1⁄4 inches. Royal sizes were used for posters and billboards.

Imperial sizes were used in the United Kingdom and its territories and some survived in US book printing.

Traditional British paper sizes

Traditional British paper sizes are referred to by the number of sheets that can be cut from a sheet of uncut paper.^[40] The standard Imperial uncut paper sizes used in offices and schools were "foolscap", "post", and "copy". Each uncut sheet can then be halved into folios, quartered into quartos, or eighthed into octavos.

Traditional French paper sizes

Before the adoption of the ISO standard system in 1967, France had its own paper size system. Raisin format is still in use today for artistic paper. All are standardized by the AFNOR.^[42] Their names come from the watermarks that the papers were branded with when they were handcrafted, which is still the case for certain art papers. They also generally exist in double versions where the smallest measure is multiplied by two, or in quadruple versions where both measures have been doubled.

Business card sizes

The international business card has the size of the smallest rectangle containing a credit card rounded to full millimeters, but in Western Europe, it is rounded to half centimeters (rounded up in Northern Europe), in Eastern Europe to full centimeters, in North America to half inches. However, credit card size, as defined in ISO/IEC 7810, also specifies rounded corners and thickness.

Newspaper sizes

Newspapers have a separate set of sizes.

• Compact: AR 1.54
• Berliner: aspect ratio is 1.5
• Rhenish: AR 1.4–1.5
• Tabloid 1.34
• Broadsheet: aspect ratio 1.25

In a recent trend^[45] many newspapers have been undergoing what is known as "web cut down", in which the publication is redesigned to print using a narrower (and less expensive) roll of paper. In extreme examples, some broadsheet papers are nearly as narrow as traditional tabloids.