A3 Paper Size: Ideal for Layouts and Proofs

Lay two A4 pages next to each other and you have an A3 sheet, which under ISO 216 measures 297 x 420 mm (11.69 x 16.54 in).

Designers and drawing offices use it for posters and technical drawings, and print shops get asked for it constantly. Wide tables that A4 can’t hold end up on it too.

Going between the two sizes takes 71% in linear terms, not 50%. Reducing A3 to A4 means 71%, and enlarging an A4 page back up takes 141%. Those are the preset magnification keys on copiers built for ISO sizes (Markus Kuhn, University of Cambridge, 2025).

What Are the Dimensions of A3 Paper?

An A3 sheet measures 297 x 420 mm under the ISO 216 A series, which is exactly twice the area of A4.

In portrait the 297 mm edge is the width. Turn it to landscape and the sheet is 420 mm wide and 297 mm tall.

• 297 x 420 millimetres
• 29.7 x 42 centimetres
• 11.69 x 16.54 inches (retail pages often round it to 11.7 x 16.5)
• 842 x 1191 points

Values follow ISO 216, with the unit conversions as listed by papersizes.io.

ISO 216 defines every size in whole millimetres, so the inch and point figures are conversions. That is why you see both 11.69 x 16.54 and 11.7 x 16.5 for the same sheet.

A finished sheet also isn’t guaranteed to hit 297 x 420 exactly. ISO 216 allows plus or minus 2 mm on dimensions between 150 and 600 mm, so a compliant A3 sheet can be 295 to 299 mm wide, while DIN 476 holds that range to plus or minus 1.5 mm (Markus Kuhn, University of Cambridge, 2025).

Design to the stated size, but keep text and logos off the outer few millimetres.

How Many Pixels Is A3 at 72, 150 and 300 DPI?

At 300 DPI an A3 sheet comes out at 3508 x 4961 pixels. At 150 DPI it’s 1754 x 2480, and 72 DPI brings it down to 842 x 1191.

The sheet stays 297 x 420 mm in every case. Only the pixel count changes.

Pixel values by resolution

The DPI value you choose sets how many pixels cover each inch of the sheet, so the calculation is inches times DPI. At 300 DPI, 297 mm is 11.69 in, which gives 3508 px (3507.9 before rounding).

Values come from Moda’s A3 reference and match Polotno and papersizes.io wherever they overlap.

Points use 72 per inch, so the 72 DPI row doubles as the point size (842 x 1191 pt). Screens count pixels per inch (PPI) and printers count dots per inch, but design tools use the two terms loosely and the maths is identical.

Published figures drift by a pixel or two. Quill lists the 300 DPI height as 4960, while Moda, Polotno and papersizes.io list 4961, which is what 420 / 25.4 x 300 = 4960.6 rounds to.

Global Sources gives 841 x 1189 at 72 DPI. That is the A0 millimetre size, not the A3 result of 842 x 1191.

Canvas size with bleed

Polotno puts the 300 DPI canvas with 3 mm bleed on every edge at 3579 x 5031 px.

That extra bleed margin is background that runs past the trim line, so the cutter never leaves a white sliver.

Stick with 300 DPI for photographs and anything with fine detail. Text-heavy pages and large posters read from a distance hold up fine at 150 DPI, and a file that never leaves a screen can stay at 72 or 96.

Don’t upscale a 72 DPI file to 300 DPI and expect sharper output. The pixels you start with are the pixels you print.

How Does A3 Fit Into the ISO 216 A Series?

Counting up from A0, A3 lands fourth. It’s half of A2, double A4, and one eighth of A0.

ISO 216 also defines the B series, and the C envelope series, formerly set out in ISO 269 (now withdrawn), follows the same logic, so A3 belongs to a family of international paper sizes that all share one aspect ratio.

Relation to A4 and A2

A4 (210 x 297 mm) has half the area of A3, so one fold turns an A3 sheet into two A4 pages. Go the other way and A2 (420 x 594 mm) has double the area, which means two A3 sheets side by side make one A2.

The long side of each size equals the short side of the next larger one. A3’s 420 mm height is the width of A2, and its 297 mm width is the height of A4.

Printers use this constantly, folding A3 sheets once to get brochures in the A4 format with no trimming.

Aspect ratio and area

A3 keeps the 1:1.414 ratio of every A size.

Only a rectangle whose long side is the square root of two times its short side keeps its shape when cut in half. That is why scaling A3 to A4 or A2 never distorts a layout.

A0 is defined as 1 m2, so A3 is nominally 0.125 m2. The rounded 297 x 420 mm sheet actually measures 124,740 mm2, or 0.1247 m2 (papersizes.org).

Each size is halved and then rounded down to whole millimetres, which guarantees two A3 sheets never exceed an A2 sheet (Kuhn, University of Cambridge, 2025).

Origin in DIN 476 and ISO 216

The ratio is older than the standard.

• Georg Christoph Lichtenberg describes the square-root-of-two ratio in a letter to Johann Beckmann in 1786.
• A French tax law from 1798 lists “moyen papier”, which matches modern A3.
• Walter Porstmann’s system becomes the German standard DIN 476 in 1922.
• ISO 216 makes it international in 1975.
• The current ISO 216 edition arrives in 2007.

The first four entries follow Markus Kuhn’s history of the standard. ISO reviewed and confirmed the 2007 edition in 2021, so it remains current.

ISO 216:2007 covers trimmed sizes for administrative, commercial and technical paper, and it does not necessarily apply to posters or newspapers, according to ISO.

How Does A3 Differ From Tabloid, A3+ and SRA3?

US Tabloid comes out 18 mm narrower and 12 mm taller than A3. A3+ and SRA3 are bigger sheets, which is what lets an A3 design run right to the edge.

Dimensions follow ASME Y14.1 for Tabloid, ISO 217:2013 for RA3 and SRA3, and Printerland’s size guide for A3+.

Tabloid, Ledger and ANSI B all name the same 11 x 17 in sheet. ASME consolidated its drawing-sheet standard as ASME Y14.1-2020.

The catch is ratio. US sizes alternate between 1.545 and 1.294, while every ISO size sits at 1.414, so A3 artwork on Tabloid stock either leaves margins or gets cropped (Markus Kuhn, University of Cambridge, 2025).

A3 is also 18 mm wider than Tabloid. A 100% print does not fit, and the printer scales it to roughly 94%.

A3+ (Super A3) is not an ISO 216 size. At 329 x 483 mm, also listed as 13 x 19 in, its ratio is 1:1.468 against A3’s 1:1.414 (papersizes.org).

The extra 32 mm of width and 63 mm of height hold a full A3 page plus annotations, which is why design and proofing work uses it (Printerland).

RA3 and SRA3 are the untrimmed sheets of ISO 217:2013 (RA is raw format A, SRA is supplementary raw format A). They exist so ink can reach the edge before the sheet is cut down.

Do the subtraction. RA3 has 4 mm spare width and 5 mm spare height per edge, which leaves 1 mm and 2 mm after a standard 3 mm bleed, against 8.5 mm and 12 mm on SRA3.

Only SRA3 leaves room for crop marks outside the bleed.

For a full-bleed job, order SRA3 and have the printer cut the sheets down to the finished trim size of 297 x 420 mm.

If you want a white border, plain A3 stock does the job. Full bleed on a desktop printer needs A3+ stock, and a US print shop will usually run Tabloid stock with the file scaled to about 94%.

What Is A3 Paper Used For?

A3 earns its size where A4 runs out of room.

• Small posters, concert flyers, menus and notices
• Engineering, architectural and science drawings
• Large tables and diagrams that turn unreadable when shrunk to A4
• Newspaper-size pages

Use cases follow Quill’s A3 guide, Adobe’s A3 format page and Markus Kuhn’s table of ISO format applications.

Posters at this size get read from a few steps away, so a clear poster design with one dominant image beats fine detail.

Drawing offices work to ISO 5457, which sets sheet sizes and layout for technical drawings from A0 to A4. It pairs every trimmed sheet with a larger untrimmed one: 880 x 1230 mm for A0 and 240 x 330 mm for A4 (ISO 5457:1999, amended 2010).

ISO 5457 lists the matching A3 sheet as A3U at 330 x 450 mm, a different raw size from the SRA3 stock used for bleed printing.

Line weights scale the same way. Technical pens come in steps of the square root of two, so a drawing inked with a 0.35 mm pen on A3 continues with the 0.25 mm pen once it is reduced to A4 (ISO 9175-1, as summarised by Kuhn).

The good side is easy to see. Drawings and type stay readable at a size you can pin to a wall, most copying machines take it alongside A4, and a C3 envelope holds it flat.

The downsides are mostly practical.

• You need a printer, copier or scanner built for the size.
• It does not fit A4 folders and binders unfolded, because folder and file sizes (ISO 623, since withdrawn) were set for A4 sheets.
• Carrying it around and storing it flat is a hassle.

How to Set Up an A3 File for Print

1. Create the document at 297 x 420 mm, portrait or landscape. In InDesign the page size is the finished size after trimming, so bleed does not go into it.
2. Set raster resolution by picking a row from the pixel table above. Illustrator’s New Document panel carries its own raster-effects resolution field.
3. Enter bleed for each side and keep key content away from the trim edge.
4. Choose the color mode your printer asks for.
5. Export a print PDF with bleed, plus crop marks if the shop wants them.
6. Open the exported PDF and confirm the bleed is there before uploading.

Behavior is as described in Adobe’s February 2026 Illustrator help page, Adobe’s InDesign help and the Canva Help Center.

Illustrator also lets you set different bleed values per side through a link icon. Canva Docs has no bleed or crop marks at all, so an A3 poster belongs in a standard Canva design.

Bleed units differ by market. A University of Wisconsin print guide gives the standard as an eighth of an inch, while metric shops quote millimetres, so enter the number your printer’s spec sheet states.

A traditional press works in the CMYK ink model, and Moda tells designers to always export CMYK for professional print.

ISO 15930-7 disagrees on the strict version of that rule. PDF/X-4 accepts colour-managed RGB, gray and spot colour data, and ISO reviewed and confirmed the standard in 2026.

The practical answer is to ask the shop. A PDF/X-4 workflow can take managed RGB, while a shop that wants flat CMYK needs the conversion done before upload.

Run the full preflight for a print-ready file before you send an A3 job, because missing bleed is cheaper to fix on your side than at the press.

When Does A3 Not Work?

Most A3 problems come from the equipment rather than the file. The sheet outgrows the printer or the scanner bed, or the software just doesn’t offer the size.

• Many home and office printers stop at A4, so A3 means a wide-format machine or a print shop (Moda).
• An A4 scanner bed forces two passes and a stitch for an A3 original.
• Word can hide A3 when the active printer driver cannot print it.
• Printers leave unprintable margins, and borderless modes often stop short of true A3.

Epson’s spec sheet shows how far labels drift. The WorkForce Pro WF-7840 takes sheets up to 13 x 19 in (A3+), but its borderless limit is listed as A3 at 11 x 17 in, which is Tabloid, not true A3 (Epson America).

Canon’s support documentation quantifies the margin cost. On its Art A3 setting for fine-art paper, the printable area is 290.2 x 350.0 mm, with a 35 mm margin at the top and bottom.

Keep logos and text inside that safe zone whenever the stock or driver restricts the print area.

In Word, A3 disappears from Layout, Size when the selected printer cannot print it, according to Microsoft Learn question threads from 2025. Enter 297 x 420 mm under Custom size, or switch the default to the Microsoft Print to PDF driver, which lists A3.

Screen-size photos are the quiet failure.

A 1920 px wide image stretched across the 16.54 in side of a landscape A3 page works out to about 116 PPI, below the draft tier in the pixel table.

Check how print and screen resolution differ before you place web images in an A3 layout.

A3 Paper Size FAQ

How much does an A3 sheet weigh?

An 80 gsm A3 sheet weighs 10 g, and a 100 gsm sheet weighs 12.5 g, according to papersizes.org.

A3 covers about 0.125 m2, so multiplying the gsm figure by 0.125 gives a quick estimate for any stock.

Which envelope fits A3 paper?

Unfolded A3 goes into a C3 envelope (324 x 458 mm).

Folded once, the sheet slips into a C4 envelope. Folded into quarters, it fits a C5.

Is A3 the same as legal size?

No. Legal is a US size of 216 x 356 mm (8.5 x 14 in), which is smaller than A3 in both directions (Markus Kuhn, University of Cambridge, 2025).

What is an A3 report in lean management?

Lean management borrows the name for a format that fits a whole problem analysis onto one A3 sheet.

Lean practitioners treat it as a thinking process rather than a document template. The sheet size works as a limit on length, not as the point.

Can you buy A3 paper in the US?

Yes, though ISO sizes are uncommon there. Specialty suppliers such as Graytex Papers stock A3, A4 and A5, according to Kuhn’s supplier list.

What to Confirm With the Printer Before an A3 Job

Before an A3 paper size job goes out, ask the printer which sheet it prints on, A3 or a larger raw one. Then get the bleed amount and color mode, and finish by checking which PDF standard it accepts and whether a proof comes first.

Each answer limits the next. The sheet fixes the bleed room, and the bleed and color spec fix how the PDF gets built.

A shop still on PDF/X-1a:2001 accepts only CMYK and spot colours (ISO 15930-1), so managed RGB needs conversion first.

Full bleed on a larger sheet buys clean edges at the cost of a trimming step. Plain A3 skips the cut and keeps a white border.

If the artwork needs more room, the A2 sheet size is the next step up.

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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.

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