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What is A4 Paper?

By EC Rosenberg
Updated May 16, 2024
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A4 paper is the standard paper size used worldwide, with the exception of countries in North America. The US, Canada, and Mexico have standardized 8.5 inch by 11 inch (about 21.5 cm by 27.9 cm) paper, typically referred to as "letter" size. A4 paper is slightly longer, at about 8.27 inches by 11.75 inches (21 cm by 29.7 cm). This and other types of "A" paper sizes are based on a metric measurement system and established through international European standards.

Basis for Different Sizes

A4 paper and similar sizes are based on metric measurements. An A0 piece of paper, when spread flat, has an area of one square meter and is the largest size at 84.1 cm by 118.9 cm (about 33 inches by 46.75 inches). A0 paper, cut in half, becomes size A1 at about 59.4 cm by 84.1 cm (or 23.38 inches by 33 inches). A1 cut in half is A2, and so on through A6.

This produces paper with different sizes, but all with a 1:1.414 height-to-width ratio. European standards also cover B paper sizes. B0 paper is a meter wide and 1.414 meters tall (about 39.37 inches by 55.75 inches); B1 is B0 cut in half, and so forth through B5.

The value of this system for paper sizes is that each size is proportionately equal to the next. A4 paper, for example, is about 21 cm by 29.7 cm (about 8.27 inches by 11.75 inches), while A3 is 29.7 cm by 42 cm (around 11.75 inches by 16.5 inches). If someone has text or images on a sheet of A4 paper and wants to enlarge it onto A3 paper, it can be done quite easily without losing any of the content of the document. This proportion, which uses the square root of two, or 1.414, is known as the Lichtenberg Ratio, named for the German physicist who first noted its usefulness.

Size and Standardization

Paper sizes were standardized in Germany in 1922, and adopted throughout Europe in 1930, via Standard 216 of the International Standards Organization (ISO). The ISO is a non-governmental entity that publishes international standards. While the standards have been updated occasionally, the sizes used have been maintained since the early 20th Century.

Paper Weight

The weight of European paper is based on the metric system and is standardized under ISO Standard 536, originally developed in 1976 and updated in 1995. European and other non-American papers are weighted based on the number of grams per square meter (g/m2) for each type of paper. A4 paper is available in most standardized paper weights; A4 printer paper's weight is 90 g/m2, while cover stock is 250 g/m2.

Alternative Sizes

North American paper continues to be determined by Imperial Measurement. Standard letter size paper in the US is 8.5 inches by 11 inches (about 21.5 cm by 27.9 cm), while legal size paper is 8.5 inches by 14 inches (around 21.5 cm by 35.56 cm). This means that someone trying to enlarge a document from letter to legal loses information because the North American format does not use a constant ratio between sizes. Engineers and other people working on international projects often use A4 paper and similar European standards to avoid confusion and make conversions simpler and more precise.

How Big is A4 Paper Compared to Letter Paper?

A4 and letter paper are both standard document sizes depending on where you live. A4 paper has an area of approximately 1/16th of a meter, which means 16 pieces of paper arranged in a square should equal one square meter, also known as an A0 document. This means the A4 paper is both longer and narrower than a letter-sized document.

On the other hand, letter paper size doesn’t come from a proportion of another measurement. It came about when people made paper by hand, and the mold measured 17x44 inches. The large sheets were then cut into eight pieces, making the products a size 8.5 x 11 inches. During the 1920s, when most other countries adopted the ISO standard-sized A4 paper, America chose to continue using their existing manufacturing system. While Canada and the United States are the only countries that officially adopted the ASMI standard letter size, this paper is commonly used in the Philippines and many South American countries.

Are A4 Paper Dimensions Different Than Letter Settings When Printing?

An A4 document measures 210mm by 297mm, while letter paper measures 215.9mm by 279.4mm. This means that printer settings are different, and creating various documents will have contrasting margins. Unfortunately, when you print a copy on the wrong-sized paper, it won’t appear the way you made it look when you typed it up.

Document Creation

Most document software and internet-based services allow you to change the format of an article. It’s always a good idea to match your document's layout to the size of your printer paper. Otherwise, your manuscript may not print in its entirety.


When creating a document using a letter format, the default margins are .75 inches for all four sides of the paper. These margins make the printable area of a letter document approximately 7 x 9.5 inches, not including a header or footer. On the other hand, American software systems set the A4 margins much larger all around. They measure one inch at the top and bottom of the page and 1.25 inches on both sides. These margins give you a printable space of 6.27 in x 9.19 in for A4 paper, which is much less area than a letter document. However, when you reduce these margins to European standards, there is 3.5% more printable space on A4 paper than letter paper.

Printing an A4 document on Letter Paper

If you have created a brochure, document or spreadsheet using an A4 format, you need to make adjustments if you want to print on letter paper. Here are a few options to consider:

  • Reformat the Document – You can go to the settings on the document and change the page layout from A4 to letter. This works well if you have a simple document without any specialized formatting.
  • Change the Article’s Margins – When you have a spreadsheet, brochure or other design that must stay in the exact layout as you created using the A4 format, then you need to adjust the margins. Since letter paper is wider, increase the side margins of your A4 document by .23 inches and decrease the top and bottom margins by .69 inches, so your information doesn’t get cut off at the bottom.
  • Change the Printer’s Settings – If you don’t want to change the document’s look, you can change the printer’s format. When the print box is open, choose "print to scale." This automatically shrinks the document to the largest margin that fits the paper. The drawback is that the print size and pictures may be smaller than you designed.

Why Is A4 Standard Paper Size Advantageous to Users?

Nearly all countries follow the ISO standard for paper size instead of the ANSI. There are many advantages to using ISO A4 paper.

  • In Europe, publishers use A4 paper for school books, encyclopedias, legal documents, magazines and brochures. This consistency makes it easier for stores and libraries to display these items because shelving is available in compatible sizes.
  • The ISO standards make it simpler to fit documents in appropriately sized envelopes and file folders.
  • A4 paper is a convenient choice for engineers and architects because the document is already precisely scaled using the metric measurement of one meter. You can create projects to scale by using millimeters and centimeters to represent one meter.
  • Documents can be shared easily between countries, both in paper form and electronically, when the countries both use ISO standards.
  • Documents created using ISO standards can be enlarged or shrunk on a copy machine or scanner without losing the original aspect ratio of data.
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Discussion Comments

By StreamFinder — On Sep 09, 2010

Thank you so much for this article -- I'm sending in a thesis prospectus to a school in Germany, and they asked for it to be printed on "white A4 inkjet paper -- I had no idea what it was, but this totally helped me out!

Thank you!

By pharmchick78 — On Sep 09, 2010

How big is A4 paper in mm? I know how much A4 paper is in inches, but what about in mm?

By gregg1956 — On Sep 09, 2010

When I was in Britain for a few months on business, I was completely baffled when somebody asked me if I wanted something printed with A4 paper measurements -- A4, A3, it all meant nothing to me.

Of course, I learned the A4 paper dimensions pretty quick though -- I guess we're just used to calling our printer A4 paper 8 1/2 by 11 over here.

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