International Paper Sizes Explained Simply

Every sheet in the ISO paper system has the same shape, a 1:1.414 aspect ratio, which is why a sheet cut in half across its longer side keeps its proportions. ISO 216 defines the A and B series, and the C series covers envelopes.

A4 (210 x 297 mm) is the office default in most countries. The United States and Canada print on Letter (8.5 x 11 in) instead.

The B series is where people get caught. ISO B5 measures 176 x 250 mm, but Japan’s JIS B5 comes in at 182 x 257 mm, according to Markus Kuhn’s reference text at the University of Cambridge (2025).

What Are International Paper Sizes?

ISO 216 sits at the center of the system, and it asks for one thing: every size in a series shares a single aspect ratio. Halve a sheet across its longer side and the pieces keep the original proportions.

Most countries use it. Markus Kuhn’s reference text at the University of Cambridge lists the United States and Canada as the industrialized exceptions, along with Mexico in part, and all of them run on inch-based sizes.

ISO 216:2007 sets the trimmed A and B series, and ISO confirmed it again in 2021 (a new systematic review opened in July 2026). ISO 217:2013 handles the RA and SRA raw sheets. The C series envelope sizes came from ISO 269, which ISO has since withdrawn, although the sizes are still in routine use.

ISO 216 only fixes the finished page. That is the trim size designers work to, the size left after the sheet is cut.

Printers start from larger untrimmed sheets. RA0 covers 1.05 square meters and SRA0 covers 1.15, against exactly 1 for A0 (ISO 217:2013).

The extra paper gives a press room to run ink off the edge as bleed before the cut. RA4 measures 215 x 305 mm and SRA4 measures 225 x 320 mm, and both get cut down to A4 after printing.

Why the 1:1.414 Aspect Ratio Lets Sheets Halve Cleanly

Divide the long side of any ISO sheet by its short side and you get 1.4142, the square root of 2. Cut the sheet in half across the long side and each half has the same ratio as the original.

Kuhn’s text puts it as the way a square’s side relates to its diagonal. That is the whole trick.

A0 is defined as one square meter, which works out to 841 x 1189 mm. A4 is one sixteenth of that at 210 x 297 mm, so a sheet weighs 5 g at 80 g/m2 (Kuhn, University of Cambridge). The 1:1.4142 ratio holds for every A, B and C size, give or take whole-millimeter rounding.

Tolerances loosen as sheets get bigger: +/-1.5 mm up to 150 mm, +/-2 mm from 150 to 600 mm, and +/-3 mm above 600 mm (ISO 216, as summarized by Kuhn).

Copiers lean on all this. One size down is 71%, one size up is 141%, and nothing gets cropped.

The square root of 2 is irrational, so a sheet can’t have whole-millimeter sides at exactly that ratio. ISO fixed the area of A0 first and rounded the sizes after.

Each size is halved from the one before and rounded down to the next lower millimeter. Two A5 sheets can therefore never measure more than one A4 sheet.

The rounding costs a little at the small end. A4 (297 divided by 210) sits at 1.4143, but A10 (37 divided by 26) drifts to 1.4231.

People sometimes confuse this with the golden ratio of about 1.618. That one holds up after you cut a square off the end. The paper ratio is the one that survives a cut straight through the middle.

A Series Paper Sizes From A0 to A10

A0 (841 x 1189 mm) is the biggest regular size and A10 (26 x 37 mm) the smallest, with each step halving the previous sheet across its longer side. Dimensions go width first, so a portrait A4 is 210 mm wide and 297 mm tall.

The big sheets mostly end up on walls and drafting tables.

Smaller sheets are what people actually hold.

Most people never handle anything but the A4 format. Kuhn’s text names it the most important size for daily office use.

An A3 sheet is two A4 pages side by side. That is why a two-page spread from an A4 journal copies onto one A4 sheet at 71%.

Further down, A7 is 74 x 105 mm (the German ID card, per Kuhn), A8 is 52 x 74 mm, A9 is 37 x 52 mm and A10 is 26 x 37 mm.

Above A0 sit 2A0 (1189 x 1682 mm) and 4A0 (1682 x 2378 mm). ISO 216:2007 counts both as rarely used members of the series.

How the B and C Series Differ From the A Series

Each B size sits halfway between two neighboring A sizes, and each C size sits halfway between the A and B sizes with the same number. Halfway here means a geometric mean, so the same scale factor steps A to B and B to the next A.

B series sizes

B0 measures 1000 x 1414 mm and B5 measures 176 x 250 mm. B1 is the geometric mean of A1 and A0, so the factor that scales A1 up to B1 also scales B1 up to A0 (Kuhn).

In Kuhn’s text, books often use B5 or B6, and newspapers use B4. Passports are B7, the US and EU ones included.

One caveat. ISO 216:2007 says it does not necessarily apply to newspapers, published books or posters, so B5 as a book size is trade practice and not an ISO requirement.

C series sizes and envelope fit

Run the formula in Kuhn’s text and every C size comes out about 9% larger than the A sheet it carries (a factor of 2 to the power of one eighth, or 1.0905). That margin is why an A4 letter slides into C4 without catching.

The DL envelope (110 x 220 mm) sits outside the C series and takes an A4 sheet folded in thirds. In ISO’s wording DL stands for Dimension Lengthwise, though it probably started as “DIN lang”.

Kuhn notes that makers found DL slightly small for automatic inserting machines. DIN 678 added C6/C5 (114 x 229 mm) as the alternative.

As of October 2026, ISO’s catalogue lists ISO 269:1985, the standard behind these envelope sizes, as withdrawn. The dimensions stay in routine use, and DIN 678 lists the same formats.

ISO B versus JIS B

Japan’s JIS P 0138 shares the A series with ISO but defines its own B series, so the same label points to a different sheet.

ISO takes the geometric mean of neighboring A sizes. That gives a B0 of 1000 x 1414 mm (about 1.41 square meters) and a B5 of 176 x 250 mm. JIS goes with the arithmetic mean instead, which makes its B0 1030 x 1456 mm at 1.5 square meters, and its B5 182 x 257 mm.

JIS B5 comes out 6 mm wider and 7 mm taller than ISO B5. Kuhn’s text recommends avoiding the JIS series because it adds magnification factors and is not an international standard. I’d skip it unless a Japanese client asks for it by name.

A printer quote for “B5” needs the standard named. Otherwise a Japanese notebook order and a European book order land on different sheets.

What Are the Standard North American Paper Sizes?

The inch-based North American sizes are led by Letter (8.5 x 11 in), with Legal (8.5 x 14 in) and Tabloid (11 x 17 in) right behind it. None of them follow the 1:1.414 ratio.

Letter, Legal and Tabloid

Letter does most of the work in US and Canadian offices. It measures 8.5 x 11 in (215.9 x 279.4 mm), a ratio of 1.2941.

Legal keeps that width and stretches to 8.5 x 14 in (215.9 x 355.6 mm). Tabloid is 11 x 17 in (279.4 x 431.8 mm), and it is sold as Ledger when the same sheet is turned to landscape.

Legal has a reputation it hasn’t earned. Kuhn calls the idea that Legal is for legal work a popular myth, and notes that most US legal documents use Letter.

ANSI and architectural sheets

ANSI/ASME Y14.1 builds engineering sheets on Letter, labeling it ANSI A and stepping up through B (11 x 17), C (17 x 22), D (22 x 34) and E (34 x 44) in inches. BSI Knowledge lists ASME Y14.1-2020, published 18 December 2020, as the current edition.

ANSI sheets nest. Cut ANSI C across its 22 in side and you get ANSI B.

The shape flips at every step, though, between a ratio of 1.2941 and 1.5455. A drawing can’t be reduced to the next size without leaving a margin (Kuhn).

Architects work from a second family. ARCH sizes run from ARCH A (9 x 12 in) to ARCH E (36 x 48 in).

Both families have a D. ANSI D is 22 x 34 in and ARCH D is 24 x 36 in, according to the paper-size reference from Rensselaer Polytechnic Institute’s IT service, so a plot job needs the series name and not only the letter.

A4 vs US Letter: What Changes When You Print

A4 is about 6 mm narrower and 18 mm taller than Letter. An A4 layout shrinks to 94% to fit Letter, and a Letter layout shrinks to 97% to fit A4, both factors coming from Kuhn’s reference text.

The shrink isn’t the bigger cost. Reflowing is. Kuhn notes that an A4 word-processing layout often loses content on Letter or needs reformatting, and reformatting changes the page numbering.

The two sheets do share a rectangle of 210 x 279.4 mm. A layout that stays inside it prints on either size with no scaling, and only the margins differ.

Publishers have used this for decades. PA4 (210 x 280 mm) was proposed in an early ISO 216 draft as an interim size, and Kuhn reports that magazines printed on both A4 and Letter presses still use it.

Acrobat’s page scaling goes the other way. Adobe’s help describes Fit To Printable Area, which scales small pages up and large pages down, and Shrink To Printable Area, which resizes only pages larger than the paper and is Acrobat’s default. Current Acrobat menus label these options Fit and Shrink oversized pages.

Staying inside the overlap doesn’t remove the printer’s own edge margin. A layout that touches the 210 x 279 mm boundary still clips where the printer can’t reach.

Legal shares Letter’s width and adds 3 in of height, so a Letter layout fits a Legal sheet at full size. A3 onto Tabloid needs 94% too, the same factor as A4 onto Letter, because Tabloid’s width (279.4 mm) equals Letter’s height.

Which Countries Use A4 and Which Use Letter?

Almost every country defaults to A4. The United States, Canada and the Philippines default to Letter, and a band of Latin American countries leans on it in practice, though published lists disagree at the edges.

Store norske leksikon, working from 2025 Unicode CLDR data, calls Letter the official default in the United States, Canada and the Philippines, and widespread in Belize, Chile, Colombia, Costa Rica, El Salvador, Guatemala, Mexico, Nicaragua, Panama and Venezuela.

The older glibc bug report 9963 (CLDR 1.7) names the United States, Canada, Puerto Rico, Venezuela, Chile, Mexico, Colombia and the Philippines. Then there is a Bolivian contributor on the CLDR-Users mailing list (April 2018) who asked to move Bolivia from A4 to Letter, calling Letter the de facto standard.

The core is stable. The United States, Canada, Mexico, Chile, Colombia, Venezuela and the Philippines appear in both CLDR-based lists.

Everything beyond that depends on data vintage, and on whether a source records an official default or what stores actually stock. Kuhn’s text limits itself to industrialized nations, so it understates the region.

Bolivia shows the gap. CLDR carried A4 for the country in 2018, yet the requester called A4 very hard to buy there.

Official adoption doesn’t settle it either. Kuhn’s adoption list has Venezuela on the ISO system in 1962, Mexico in 1965, Chile in 1968 and Colombia in 1975, and all four still appear as Letter countries.

Store norske leksikon puts the staying power down to contact with the United States. It adds that Letter use has been falling steadily outside the US and Canada.

Software follows the region. Microsoft Word picks its default paper from the Windows regional settings active at installation, according to Office Watch (2020), so a Word file arrives in its author’s regional size.

As for why the US kept Letter, no standards body chose it.

Kuhn traces Letter to a 1921 committee of printing-industry representatives that recommended 17 x 22 in basic sheets, and Letter is that sheet halved. He reads it as a commercial compromise that cut inventory without retooling presses, and records a hypothesis that hand-made paper mold sizes shaped it.

The federal government ran on 8 x 10.5 in until January 1980, when it moved to Letter, according to Kuhn. Store norske leksikon also dates the switch to 1980.

Where Did the ISO Paper Size System Come From?

ISO 216 arrived 189 years after the idea first appeared on paper. Lichtenberg described the ratio in 1786. Walter Porstmann built it into DIN 476 in 1922, and ISO published the first ISO 216 in 1975.

Lichtenberg’s letter is dated 25 October 1786. The Goettingen physics professor Georg Christoph Lichtenberg wrote to Johann Beckmann that a sheet’s short side should relate to its long side like the side of a square to its diagonal, and he added that ordinary writing paper already had that shape.

France’s Loi sur le timbre (no. 2136), dated 3 November 1798, taxed paper by formats that match modern A2, A3, B3, B4 and B5. The series was soon forgotten, per Kuhn.

Porstmann reinvented it independently in 1922, and it became DIN 476, the German standard that replaced a wide range of earlier formats. “DIN A4” is still the everyday name in Germany and Austria, according to the NRICH project at the University of Cambridge.

From there the series spread country by country, going by Kuhn’s adoption list. Belgium took it up in 1924 and Switzerland in 1929, then Japan in 1951, the United Kingdom in 1959 and Australia in 1974.

In 1975 ISO 216 became the international standard and the official United Nations document format. ISO later withdrew that edition, and the 2007 replacement adds the indication of machine direction to its title.

By 1977, 88 of 148 countries already used the A series for letters, according to a study by a German car manufacturer that Kuhn cites from Helbig and Hennig (1988).

The German original was stricter. DIN 476 sets tolerances 0.5 to 1 mm tighter than ISO 216 in each of the three size bands (Kuhn).

How to Convert Paper Sizes to Inches, Points and Pixels

Divide millimeters by 25.4 to get inches. Multiply inches by 72 for PDF points, or by your resolution for pixels, so A4 becomes 595 x 842 points or 2480 x 3508 pixels at 300 ppi.

PDF points are inches times 72. ISO 32000-2 (section 8.3.2.3) sets the default user space unit at 1/72 inch, and the page’s MediaBox stores the size in those units. CSS pixels are inches times 96, because the CSS specification defines 1 in as 96 px. For print pixels, multiply inches by the resolution in pixels per inch.

A pixel carries no physical size until a resolution is attached, which is why the DPI setting changes the pixel count of the same sheet.

For a one-off size, an mm to px converter runs the same arithmetic at a fixed resolution.

Exact A4 in points is 595.28 x 841.89, which PDF libraries round to 595 x 842. Sources also disagree by a pixel or two elsewhere. Global Sources lists 1755 and 3510 for A4’s height at 150 and 300 ppi, while the formula gives 1754 and 3508.

CSS paged media takes the same names. MDN lists A4, B5, JIS-B5, JIS-B4, letter, legal and ledger as values for the @page size descriptor (marked Baseline 2024), and it keeps ISO B5 and JIS-B5 as separate keywords.

How to Choose a Paper Size and Prepare One File for A4 and Letter

Match the size to the job first: A4 or Letter for documents, A5 for booklets, A3 or Tabloid for large tables. Then build any file that must travel between regions inside the 210 x 279 mm overlap.

Choosing a size by job

Letters, forms and reports go on A4 in most countries and on Letter in the US and Canada. Booklets and note pads fit A5, or Half Letter (5.5 x 8.5 in) in North America. Large tables and drawings want A3 or Tabloid.

Posters vary the most, since they depend on whatever the printer trims to. Check the printer’s trim against a list of common poster sizes before you set the artboard.

Preparing one file for both A4 and Letter

Treat the 210 x 279 mm overlap as the paper. Inside it, keep a safe zone for text, because printers can’t reach the sheet edge.

1. Set the page or artboard to 210 x 279 mm, or keep all content inside that box on a larger page.
2. Keep text and logos inside a margin wider than your printer’s unprintable edge.
3. Export the PDF at the page size you set, about 595 x 791 points.
4. Check scaling in the print dialog: Acrobat’s default, Shrink To Printable Area (Shrink oversized pages in current menus), resizes only pages that exceed the paper.
5. Print one copy on the paper actually loaded in the tray and inspect the edges.

Word adds its own layer. Microsoft Support says Word may scale printouts to the default paper size when you print on a different one, and the option sits under File, Options, Advanced, Print as Scale content for A4 or 8.5 x 11 paper sizes.

Office Watch (2026) reports that the option is on by default. Black Ice’s printer-driver documentation adds that Office resizes pages to the printer’s selected size whenever that size is Letter or A4, so check the tray setting too.

This approach breaks down when a US client requires Letter, or when a press is fixed to RA stock. A shared-size file is useless there, so deliver one native A4 file and one native Letter file instead.

International Paper Sizes FAQ

What are 2A0 and 4A0 paper sizes?

Both sit above A0. 2A0 holds 2 square meters and 4A0 holds 4, so the prefix simply multiplies A0’s single square meter.

How is Ledger different from Tabloid?

Only orientation separates them. Tabloid is the portrait 11 x 17 in sheet and Ledger is the landscape one, according to Store norske leksikon.

CSS uses a single ledger keyword and sets orientation separately (MDN).

Which paper size does Microsoft Word use by default?

It depends on the Windows regional settings active when Office was installed, so a US install gets Letter and most others get A4.

Change it under Layout, Size, More Paper Sizes, then choose Set As Default (Office Watch, 2020).

Can a DL envelope hold a sheet without folding it?

Yes, if the sheet is a third of A4. Kuhn’s text lists 99 x 210 mm as the common reduced-letterhead format that fits a DL envelope flat.

Anything larger needs folding in thirds.

Is Legal size used outside the United States?

Rarely, and mostly where Letter is already common. Office Watch (2024) places Letter, Legal and other US sizes across North America, almost all of Central America, Colombia, Venezuela, Chile and the Philippines.

Kuhn adds that North American sizes are hard to find outside those regions.

Confirming the Paper Size Before Files Go Out

Ask the printer or recipient which sheet they load before exporting, because international paper sizes split by region and a locale default doesn’t prove what an office stocks.

Start with the standard and size by name, such as A4, Letter or JIS B5. Then get the trim size and bleed from the printer, and finish with one proof on the paper in the tray.

A wrong name invalidates every later measurement, while the proof is the only step that spends paper.

The shared 210 x 279 mm layout is the trade-off for an unknown recipient. It fits both sheets but leaves unused paper on each, so native files win once the size is known.

This was last checked in October 2026, so a changed CLDR default or a revised ISO 216 means it needs another look.

After confirmation, setting up a print-ready file covers the remaining export checks.

• Author
• Recent Posts

Bogdan Sandu

Bogdan Sandu is a seasoned designer who has been designing websites since 2008.

Renowned for his expertise in logo design and visual branding, Bogdan has developed a multitude of logos for various clients.

His skills extend to creating posters, vector illustrations, business cards, and brochures. Additionally, Bogdan's UI kits were featured on marketplaces like Visual Hierarchy and UI8.

He also wrote in the past years on sites like Design Your Way, WebDesignerDepot, WPDean, Designmodo, Speckyboy, Slider Revolution, and more.

Latest posts by Bogdan Sandu (see all)

• The Windsurf Logo History, Colors, Font, And Meaning - 10 October 2026
• How to Remove Background From Product Photos (No Photoshop) - 10 October 2026
• How Designers can Build a Stronger Online Creative Identity - 9 October 2026