A4 size in cm is 21 × 29.7 cm (210 × 297 mm), the everyday printer-paper dimension set by the international ISO 216 standard used in most countries outside North America. That single pair of numbers is what designers, students, and office workers reach for whenever they set up a Word document, pick a frame size in Photoshop, place an order with a print shop, or check whether a downloaded PDF will print at the right scale. Because the value is defined in millimetres and the centimetre is simply ten millimetres, the conversion is exact: 210 mm = 21 cm wide, and 297 mm = 29.7 cm tall. Both values are also written as 21.0 by 29.7 centimetres, since the standard rounds to the nearest whole millimetre. If your tool, template, or export dialog asks for the width and height in centimetres rather than millimetres or inches, those two numbers are exactly what it needs. The reference table further down this page shows A4 alongside every other A series size in cm, mm and inches for quick comparison.
Most readers who land on this page are checking a specific number before they commit to a canvas size, a print order, or a layout decision. Some want a quick comparison with US Letter to see whether a downloaded form will fit. Others want to know how many pixels wide A4 becomes at 300 DPI for a print-ready file, or at 72 DPI for a screen PDF. A paper size chart that lists every standard size in mm, cm, and inches — and pairs that table with a live DPI-to-pixels converter — answers all of these questions from one screen, without juggling calculators or unit converters. The sections that follow show the official A series values, explain why A4 has those exact dimensions, walk through the four steps to look up or convert any paper size with a single tool, and compare A4 with the closest North American sheet.
A Series Paper Sizes in cm, mm and Inches
The A series is the international default for printer paper, photocopier paper, stationery, and most business documents. Every A size shares the same height-to-width ratio of about 1.414 (the square root of two), which is what lets a sheet fold in half across its longer side to produce the next smaller size with identical proportions. The table below lists every A size in the three units most workflows expect: millimetres, centimetres, and inches, all attributed to the ISO 216 standard. Width is listed first to match the order software dialogs and print specs use.
| Size | Millimetres (mm) | Centimetres (cm) | Inches |
|---|---|---|---|
| A0 | 841 × 1189 | 84.1 × 118.9 | 33.1 × 46.8 |
| A1 | 594 × 841 | 59.4 × 84.1 | 23.4 × 33.1 |
| A2 | 420 × 594 | 42.0 × 59.4 | 16.5 × 23.4 |
| A3 | 297 × 420 | 29.7 × 42.0 | 11.7 × 16.5 |
| A4 | 210 × 297 | 21.0 × 29.7 | 8.27 × 11.69 |
| A5 | 148 × 210 | 14.8 × 21.0 | 5.83 × 8.27 |
| A6 | 105 × 148 | 10.5 × 14.8 | 4.13 × 5.83 |
| A7 | 74 × 105 | 7.4 × 10.5 | 2.91 × 4.13 |
| A8 | 52 × 74 | 5.2 × 7.4 | 2.05 × 2.91 |
| A9 | 37 × 52 | 3.7 × 5.2 | 1.46 × 2.05 |
| A10 | 26 × 37 | 2.6 × 3.7 | 1.02 × 1.46 |
The centimetre column is simply the millimetre column divided by ten, and the inch column is the millimetre column divided by 25.4 (since one inch is exactly 25.4 mm). Both are exact restatements rather than independent measurements, which is why the cm values read as clean decimals and the inch values are the universally published ISO figures.
How the ISO 216 Standard Defines A4
The dimensions of A4 are not arbitrary. They come from the ISO 216 standard, the same rulebook that defines every A and B series sheet used outside North America. The standard is anchored by A0, a sheet whose area is almost exactly one square metre and whose sides measure 841 × 1189 mm. Because ISO 216 fixes the aspect ratio at the square root of two (approximately 1.414), every subsequent A size can be reached by halving the previous sheet across its longer side. A1 is A0 folded once, A2 is A1 folded once, and so on. Four folds from A0 lands on A4 at 210 × 297 mm, or 21 × 29.7 cm. That same √2 ratio is why an A4 sheet fits perfectly into a C4 envelope, and why an A4 design scales up to A3 or down to A5 without distortion — the proportions stay identical at every step.
Defining the size in millimetres rather than centimetres is a convention inherited from the German DIN 476 standard that ISO 216 grew out of in the 1920s. Because 1 cm equals exactly 10 mm, the centimetre values are always whole or single-decimal numbers, which is why 21 × 29.7 cm reads so cleanly in software dialogs that prefer centimetres over millimetres. That clean decimal pattern carries through the whole series: A3 is 29.7 × 42.0 cm, A5 is 14.8 × 21.0 cm, and so on, all the way down to A10 at 2.6 × 3.7 cm.
Look Up A4 in cm with the Paper Sizes Chart
The fastest way to confirm A4 in centimetres — or any other paper size — is to use the Paper Sizes Chart, which pairs a complete A, B and US reference table with a live DPI-to-pixels converter. The full list of sizes sits above the converter so you can scan and copy values without typing anything; the converter handles the pixel math for whatever resolution your project needs.
- Open the Paper Sizes Chart and scan the reference table to locate A4 in the A series row. The same row shows the width and height in millimetres, centimetres, and inches side by side.
- Copy the centimetre value (21.0 × 29.7 cm) if your canvas setup, export preset, or print spec is set to centimetres.
- Switch to the converter section and pick "A4" from the paper size dropdown to load the exact 210 × 297 mm dimensions into the input fields.
- Type the resolution you need in the DPI field — 300 for high-quality print, 150 for everyday office printing, or 72 for screen previews — and read off the pixel width and height instantly. The result sits next to the mm, cm, and inch values so you can grab every unit from one row.
Because the chart runs entirely in your browser, you can keep the page open as a reference while you set up a document, prepare a print-ready PDF, or sanity-check an export before sending it to a printer. Nothing is uploaded and no sign-in is required.
A4 in Pixels at Common DPIs
Designers and print buyers tend to think in paper sizes but set canvas sizes in pixels. The bridge between the two is DPI (dots per inch): pixel width equals the width in inches multiplied by the DPI, rounded to the nearest whole pixel. Because 1 inch is defined as exactly 25.4 mm, the conversion follows a single formula — millimetres divided by 25.4 to get inches, then multiplied by the DPI. The Paper Sizes Chart applies that formula automatically once you pick A4 and type a DPI, so you do not have to do the arithmetic by hand.
For typical workflows, A4 lands at 2480 × 3508 pixels at 300 DPI (the print standard), roughly 1240 × 1754 pixels at 150 DPI (good for general office printing), and 595 × 842 pixels at 72 DPI (the classic screen value used by PDF page previews and many on-screen templates). If you need an exact figure for an unusual DPI — say 200, 240, or 600 — type that number into the converter rather than approximating, since the rounding matters at high resolutions. As a quick worked example, A4 width at 300 DPI is 210 mm ÷ 25.4 × 300 = 8.2677 × 300, which rounds to 2480 pixels — and the height at 297 mm ÷ 25.4 × 300 = 11.6929 × 300 rounds to 3508 pixels.
A4 vs US Letter: Why They Don't Match
North America uses its own paper conventions set by ANSI rather than ISO 216. US Letter measures 8.5 × 11 inches (215.9 × 279.4 mm), US Legal measures 8.5 × 14 inches (215.9 × 355.6 mm), and Tabloid (also called Ledger) measures 11 × 17 inches (279.4 × 431.8 mm). Because these are defined in inches, their millimetre values are exact conversions rather than round numbers, which is why Letter and A4 end up close in size but never identical.
A4 is slightly narrower than Letter (210 mm against 215.9 mm — a gap of about 6 mm) and slightly taller (297 mm against 279.4 mm — about 17 mm more). In practice, that mismatch is small enough that text and images often fit, but margins shift and a designed-for-Letter form can clip content when printed on A4, and vice versa. If you are preparing a file that will move between regions — for example, a contract template used by both US and European teams — set the canvas to the size the final recipient expects rather than relying on auto-fit. The Paper Sizes Chart lists both the A series and US group on the same page, so you can copy the precise mm, cm and inch values for whichever sheet you need without flipping between tabs.
When You Need A4 in Centimetres
The most common situations where the centimetre value matters rather than the millimetre or inch value are: setting up a document in software that defaults to centimetres (many European releases of Word, Pages, and LibreOffice fall into this); choosing a frame or mat size in centimetres on a design tool; filling out a print order form that lists paper dimensions in centimetres; confirming that a downloaded poster, certificate, or PDF template matches your regional paper stock; and teaching or memorising the value, since 21 × 29.7 cm is one of the easiest metric paper dimensions to remember. In every case the value is the same: 21.0 cm wide and 29.7 cm tall, with a 1.414 aspect ratio preserved from A0 down to A4 and beyond. A free browser-based chart that lists all standard sizes in mm, cm, and inches alongside live pixel conversions removes the need to remember conversions or type values from memory.