A4 Paper Size: The World’s Most Popular Sheet

Most of the world prints on a sheet that measures 210 x 297 mm (8.27 x 11.69 in). That’s A4, part of the ISO 216 A series, and it is the default document page in most countries outside North America.

US Letter, at 8.5 x 11 inches, is the main alternative. It is about 6 mm wider and 18 mm shorter, which is why documents shift when they cross borders.

The published numbers describe an ideal sheet. ISO 216 allows plus or minus 2 mm on dimensions from 150 to 600 mm, so a compliant A4 sheet measures anywhere from 208 to 212 mm wide (Markus Kuhn, University of Cambridge, 2025).

What Is the Size of A4 Paper?

The short side of an A4 sheet is 210 mm and the long side is 297 mm, which works out to 21 x 29.7 cm or 8.27 x 11.69 in.

Rotate the sheet and the same numbers read 297 x 210 mm in landscape.

For one sheet, the full set of figures looks like this.

• 210 x 297 millimeters
• 21.0 x 29.7 centimeters
• 8.27 x 11.69 inches
• An aspect ratio of 1:1.414 (the square root of 2)
• A nominal area of 0.0625 square meters, one sixteenth of A0

Values follow ISO 216 as tabulated by Markus Kuhn (University of Cambridge, 2025). Inch values are conversions at 25.4 mm per inch, so they carry rounding.

Both 210 and 297 are rounded. The A series formula gives roughly 210.2 x 297.3 mm for A4.

ISO 216 starts from A0 (841 x 1189 mm) and halves it step by step, rounding down to whole millimeters each time. That rounding guarantees that two A5 sheets never add up to more than one A4 sheet.

It also explains the real area. 210 x 297 mm works out to 0.06237 square meters, a touch under the nominal 0.0625.

How Big Is A4 in Pixels and Points?

A4 has no pixel size of its own. The numbers change with resolution, from 595 x 842 at 72 ppi up to 2480 x 3508 at 300 ppi.

A PDF page sets its size in user space units, and the default unit is 1/72 inch (ISO 32000), which sits close to the typographic point. A4 comes to 595.28 x 841.89 points, and software rounds that to 595 x 842.

On the CSS side, the W3C CSS Values and Units Level 4 working draft (March 2024) fixes 1 inch at 96 px and 1 point at 1/72 inch, so 1 px equals 0.75 pt. If you’re converting CSS pixels to points, multiply by 0.75.

Print resolution measured in dots per inch only means something once the physical size is fixed. For A4 that size is 210 x 297 mm, so a 300 ppi file needs 2480 x 3508 pixels to cover the full sheet.

For screen layouts, 794 x 1123 is plenty. A mockup built at 2480 x 3508 eats memory and gains nothing unless the file is headed to a printer.

One catch on screens. The W3C draft anchors the pixel to a reference pixel, so a CSS inch on a phone or monitor rarely measures a physical inch.

Why Does A4 Have a 1:1.414 Ratio?

Height divided by width on A4 comes out at the square root of two, 1.4142, and that is why a halved sheet keeps its proportions. Cut an A4 sheet parallel to its short side and each piece is an A5 sheet with the same 1:1.414 ratio.

How the A series halves

Every format in the series has a height equal to its width times the square root of two. A0 is defined as one square meter, and cutting any size in half across its longer side gives the next size down.

Each cut halves the area, which makes A4 one sixteenth of A0. Sixteen A4 sheets fill one square meter of paper (Markus Kuhn, University of Cambridge).

Fold an A4 sheet once across its middle and you get an A5 sheet with identical proportions.

What the ratio means in practice

Copiers designed for ISO sizes usually provide keys for 71% (A3 to A4) and 141% (A4 to A3), according to Markus Kuhn. Both numbers come straight from the square root of two.

Two A4 journal pages side by side make an A3 spread. Reduce that to 71% and both pages land on one A4 sheet with no margin lost and nothing cut off.

People mix the A series ratio up with the golden ratio (1.618) fairly often. The golden ratio is what stays in proportion after you cut a square off a rectangle. The A series ratio is only about halving.

Where Does the A4 Standard Come From?

DIN 476, a German standard adopted in 1922, is where A4 comes from, and it became the international standard ISO 216 in 1975. The idea is older. Georg Christoph Lichtenberg described the square root of two ratio in 1786.

From Lichtenberg to DIN 476

• Lichtenberg, a physics professor at the University of Göttingen, wrote to Johann Beckmann on 25 October 1786 about the ratio, and noted that paper with that shape was already common.
• In 1798, France published the “Loi sur le timbre”, a paper tax law whose formats already match modern sizes (“grand registre” equals A2, “moyen papier” equals A3).
• Dr. Walter Porstmann’s A, B and C series became DIN 476 in 1922 and replaced a wide variety of older formats.
• Belgium adopted it in 1924, Japan in 1951, the United Kingdom in 1959 and Australia in 1974.

The French sizes were forgotten. Porstmann reached the same design independently more than a century later (Markus Kuhn, University of Cambridge).

ISO 216 and its companion standards

ISO 216 defines the trimmed A and B series, and A4 is its office default.

The first edition dates from 1975. ISO lists ISO 216:2007 (Edition 2) as the current edition. It was last confirmed in 2021 and entered systematic review in July 2026 (as of October 2026).

The scope covers administrative, commercial and technical paper, plus forms and catalogues. It does not necessarily apply to newspapers, published books, posters or other special items.

ISO 269 defined the C series envelopes. A flat A4 sheet fits a C4 envelope, and one folded once fits C5. ISO withdrew that standard in 2009 without naming a replacement, although Kuhn’s reference tables still list the C series sizes. ISO 217 covers untrimmed RA and SRA stock, where RA4 measures 215 x 305 mm before the printer trims it.

These standards cover the path from raw stock to a finished envelope, with the caveat that ISO 269 is no longer in force. For the full range, see the guide to international paper sizes.

Adoption was well advanced by 1977. A survey by a large German carmaker of its incoming mail found that 88 of 148 countries already used the A series (Helbig and Hennig, 1988, as reported by Kuhn).

How Does A4 Differ From US Letter?

A4 is about 6 mm narrower and 18 mm taller than US Letter, so a document built for one needs rescaling or reflowing on the other. Letter measures 8.5 x 11 inches (216 x 279 mm) in Markus Kuhn’s reference tables.

Why the two series do not scale into each other

US formats don’t halve cleanly the way the A series does.

Kuhn notes that they alternate between two aspect ratios, 17/11 (1.545) and 22/17 (1.294), so reducing one format to the next always leaves an empty margin. An aspect ratio calculator will confirm either number from a sheet’s width and height.

Which scale factor to use when printing across the two

Printing A4 onto Letter calls for 94%, because height is the limit (279.4 mm of Letter against 297 mm of A4). Letter onto A4 is 97%, and there the width is what runs out (210 mm of A4 against 215.9 mm of Letter).

Not every guide agrees. Linearity’s A4 page guide recommends 97% for printing A4 on Letter as well, which clips the bottom of the page by about 9 mm (297 mm x 0.97 = 288.1 mm, against 279.4 mm of Letter height).

Kuhn’s 94% follows from the height limit, and the arithmetic backs it.

Word makes the call for you, mostly. Microsoft Support describes automatic scaling between A4 and 8.5 x 11 inch paper, controlled by the Scale content for A4 or 8.5 x 11 inch paper sizes option under File > Options > Advanced > Print, which Office Watch reports is on by default in Word for Windows.

Which Countries Use A4, and What Is It Used For?

Nearly every country uses A4 as its default office sheet. The main exceptions are the United States, Canada, a group of Latin American territories and the Philippines.

Unicode’s CLDR territory data (release 48) lists US Letter for Belize, Canada, Chile, Colombia, Costa Rica, El Salvador, Guatemala, Mexico, Nicaragua, Panama, the Philippines, Puerto Rico and Venezuela, alongside the United States.

Sources frame the exceptions differently. Kuhn names only the United States, Canada and, in part, Mexico as industrialized nations where ISO sizes are not yet widely used.

The two lists measure different things. Kuhn tracks national adoption of ISO 216, while CLDR records the sheet size that software assumes by default for a territory.

What A4 is used for

Letters, forms, magazines, catalogs and laser printer or copier output all run on A4. Folded in thirds, a sheet fits a DL envelope (110 x 220 mm), the most widely used business letter format. Folded twice into quarters (A6 size), it fits a C6 envelope (114 x 162 mm), which suits small mailings. Kuhn’s application and envelope tables list these uses.

For print design, A4 also sits among the standard flyer sizes, next to A5 and DL.

How to Set A4 Page Size in Word, Google Docs, Photoshop, Canva and CSS

Set the page size before adding any content, then confirm the sheet reads 210 x 297 mm. Every tool buries the option in a slightly different place, so the details are below.

Converting an existing Letter document goes like this.

1. Change the paper size before editing anything else.
2. Reset the margins for the new sheet.
3. Resize images to the new printable width (the A4 page is 21 cm wide).
4. Recheck page breaks, headers and page numbers.
5. Print at 100%, or turn off automatic A4 and Letter scaling if the output still comes out as Letter.

Office Watch advises changing the paper size before writing, and warns that a reformatted document can look quite different even between two similar sizes like A4 and Letter.

Word and Google Docs

In Word, open Layout > Size and pick A4, or choose More Paper Sizes for a custom value. Office Watch reports that the default sheet follows the Windows regional settings in place when Office was installed, so a machine set up under US settings starts new documents on Letter. That one catches people out.

In Google Docs, go to File > Page setup, select Pages, then set Orientation, Paper size and Margins. Google’s help page notes these options are unavailable in pageless format, and Set as default applies the choice to new documents.

Photoshop and Canva

In Photoshop, pick Create new, then the Print tab, then the A4 preset. The file opens at 300 ppi.

Canva has no A4 preset to click. Choose Custom size, switch Units to mm, and type 210 and 297.

Photoshop’s 100% zoom shows one image pixel per screen pixel, so the sheet looks far larger than A4 on screen. View > Print Size shows it at printed size, according to an Adobe Community expert answer from 2017.

If a tool accepts only pixels, a millimeter-to-pixel converter turns those values into pixels at the resolution you need.

CSS print stylesheets

One rule sets the sheet, @page { size: A4; }.

Add landscape to rotate it, as in size: A4 landscape. MDN marks the size descriptor as Baseline 2024, meaning it works across the latest browsers since December 2024, and warns that older browsers might not honor it.

Margins, bleed and orientation

Keep margins at or above the printer’s minimum. Epson’s printable-area pages for several WorkForce and Expression models list 3 mm for normal single-sheet printing.

InDesign treats 0.125 in (3 mm) as the standard bleed, and Adobe notes some print providers need more. Set it under File > Document Setup > Bleed and Slug, then export Adobe PDF (Print) with crop marks and the document bleed settings.

The bleed area is artwork that runs past the trim edge, so it gets cut off by design.

Orientation flips with a width and height swap in a Photoshop preset. Docs has a Landscape option, and in CSS you add the landscape keyword.

The two 3 mm figures collide. Artwork that bleeds to the edge can’t print on a device with a 3 mm minimum margin in normal mode, so full-bleed jobs go to a commercial printer or a borderless setting.

When Do A4 Measurements Not Match the Sheet in Your Hands?

A real A4 sheet or printout rarely lands exactly on 210 x 297 mm.

Cutting tolerance accounts for part of it. ISO 216 allows plus or minus 2 mm on dimensions from 150 mm up to 600 mm, so a compliant A4 sheet runs 208 to 212 mm wide and 295 to 299 mm tall. DIN 476 narrows the band to plus or minus 1.5 mm for the same size range, according to Kuhn.

Printers add their own loss. The printable area is smaller than the sheet, with a 3 mm minimum margin on the Epson models above.

Then there’s rounding between units. A4 at 72 ppi is 595.28 x 841.89 points, so storing 595 x 842 moves the right edge by 0.28 points, about 0.1 mm.

A 3 mm printer margin and a 2 mm cutting tolerance together set a practical limit. Keep text and logos inside a safe zone at least 5 mm from every edge, which is a rule of thumb rather than a standard.

Pixel and point values are plain arithmetic. The sheet and the printer are where the millimeters go missing.

A4 Paper Size FAQ

How much does an A4 sheet weigh?

A standard sheet weighs 5 g. The usual office grade is 80 g/m², and A4 covers one sixteenth of a square meter, according to Markus Kuhn (University of Cambridge).

The same sheet in 100 g/m² stock weighs about 6.2 g.

Is A4 the same as DIN A4?

Yes. DIN A4 and A4 are the same 210 x 297 mm sheet, and the prefix points to DIN 476, the German standard that ISO 216 grew from.

The prefix also survives in the DL envelope, whose name probably began as DIN lang before ISO 269 recast it as Dimension Lengthwise.

Can a US printer print on A4 paper?

Yes, in most cases. Kuhn reports that practically all laser printers and copiers sold in the US support A4 as a standard feature, so selecting A4 in the print dialog is usually enough.

Finding the paper is the harder part, since he describes A4 stock as a specialty item at US stationers.

How many sheets are in a ream of A4?

A ream of A4 holds 500 sheets, the count used in the A4 retail listings Kuhn cites, such as OfficeMax’s multiuse copy paper.

At 5 g a sheet, one ream weighs about 2.5 kg.

Checking A4 Files Before They Cross a Border

Before an A4 file goes to a printer in another country, look at the page size stored in the file. Scaling can’t repair a file that was saved as Letter, so this goes first.

Next comes the scale mode at the printer. After that, print one test page and measure it with a ruler. It costs a single sheet and catches whatever the first two checks missed.

Skipping the scale step has a measurable price. An unscaled A4 page loses about 18 mm at the bottom on Letter paper, six times a 3 mm printer margin. Fitting it at 94% instead shrinks 11 pt text to about 10.3 pt, the trade-off for keeping every line.

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Bogdan Sandu

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

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