A paper size chart puts every standard sheet dimension in one place, so you never have to guess whether A4 is bigger than Letter or how many pixels wide a poster needs to be. The international A series is built around a single rule: every sheet keeps a height-to-width ratio of the square root of two, which is why A4 measures exactly 210 by 297 millimetres. The same chart pulls in the B series and the North American Letter, Legal, and Tabloid sizes, lists every dimension in millimetres, centimetres, and inches, and adds a live converter so the same sheet appears in pixels at whatever resolution you choose. That combination is what makes a chart like the Paper Sizes Chart useful for everyone who sets up documents, exports images for print, or builds PDF templates. The √2 ratio is the engine behind the whole A system: fold an A0 sheet in half along its longer side and you get two A1 sheets, fold an A1 and you get two A2 sheets, and so on down to A10, with every size holding its proportions. Because A0 is defined to cover almost one square metre, every value in the series falls out as exact halves of that anchor, which is why the numbers look so clean. North America sidesteps this system with its own ANSI-based sizes, so a chart that covers both camps lets designers and print buyers stop swapping between two different conventions mid-project.
The A Series and the Square Root of Two Rule
The A series is governed by ISO 216, the international paper standard used almost everywhere outside the United States and Canada. Its anchor is A0, defined to cover an area of one square metre. Because of the chosen aspect ratio, A0 measures 841 by 1189 millimetres. Halve A0 along its longer side and you get exactly two A1 sheets, each 594 by 841 mm. Halve again for A2 at 420 by 594 mm, again for A3 at 297 by 420 mm, and once more for A4 at 210 by 297 mm, the everyday sheet used in offices worldwide. From there the series keeps halving to A5, A6, A7, A8, A9, and A10.
The defining trick is the aspect ratio. Every A sheet has a height-to-width ratio of about 1.414, the square root of two. That single property is what makes the series so useful for documents: scaling from A4 to A3, or down to A5, preserves the proportions of whatever is on the page, so text, images, and margins all keep their relative size. Photocopiers and printers lean on this every time you choose "A4 to A3 enlarge": the page doubles in size without distortion. The chart below lists the official ISO 216 dimensions for the A sizes most people reach for, in millimetres.
| A Series | Dimensions (mm) | Dimensions (in) |
|---|---|---|
| A0 | 841 × 1189 | 33.1 × 46.8 |
| A1 | 594 × 841 | 23.4 × 33.1 |
| A2 | 420 × 594 | 16.5 × 23.4 |
| A3 | 297 × 420 | 11.7 × 16.5 |
| A4 | 210 × 297 | 8.3 × 11.7 |
| A5 | 148 × 210 | 5.8 × 8.3 |
| A6 | 105 × 148 | 4.1 × 5.8 |
Centimetre and inch values fall directly out of the millimetre values, so once you have the mm row you can read any unit off the same chart without doing the arithmetic yourself.
The B Series: Sized to Sit Between the A Sizes
When an A size is just a bit too small and the next A size up is just a bit too large, the B series fills the gap. The B sizes are defined alongside the A series under ISO 216, with B0 anchored at 1000 by 1414 millimetres. B1 comes in at 707 by 1000 mm, B2 at 500 by 707 mm, and so on, halving down to B10 just like the A series does. The B sheet at any given level sits geometrically between the matching A sheet and the next larger A sheet, which is what makes B sizes so useful for the awkward in-between dimensions that come up in print and stationery design.
B5 is the page size most paperbacks use. B4 is a common poster size when A3 feels too small and A2 feels too large. B-series envelopes wrap A-series inserts with a slightly looser fit than an exact A envelope would, which is why the ISO defined them in the first place. A full paper size chart lists B0 through B10 alongside the A and US sizes so you never have to derive the midpoint values by hand.
North American Sizes: Letter, Legal, and Tabloid
Outside the ISO system, the United States and Canada use ANSI-defined sizes that look close to A sizes at first glance but never quite line up. The three sizes any print job is likely to need are US Letter at 8.5 by 11 inches, the default page size in Word and the default in most North American office printers; US Legal at 8.5 by 14 inches, used for legal pads and longer contracts; and Tabloid, also called Ledger, at 11 by 17 inches, the standard for spreadsheets, brochures, and small posters.
These sizes are defined in inches, so their millimetre values come out as exact conversions: 8.5 × 25.4 equals 215.9 mm, and 11 × 25.4 equals 279.4 mm. That tail of decimals is why A4 and Letter never match up exactly: A4 is 210 by 297 mm, slightly narrower and a little taller, so a document formatted for one won't sit on the other without a margin shift. A complete paper size chart always shows the inch values alongside the millimetre values, because printers and PDFs in North America default to inches while European software defaults to millimetres, and the chart has to translate between them.
Why Every Chart Shows mm, cm, and Inches Side by Side
A paper size chart only earns its place if the units match what your software or printer expects, which is why every useful chart shows all three. Millimetres are the official ISO unit and the default in spreadsheets, CAD tools, and most European print software. Centimetres are the everyday unit taught in schools and used in school reports, posters, and casual design work, with one centimetre equal to 10 millimetres exactly. Inches are the North American default and the language of every US-bound printer, defined against the millimetre by the exact constant 1 inch equals 25.4 mm.
The math between them is short. Millimetres to inches is division by 25.4, millimetres to centimetres is division by 10, and inches to millimetres is multiplication by 25.4. Because these are defined as exact constants rather than measured values, you can convert any dimension on the chart by hand if you ever need to, and you will land on the same number the chart shows. The reference table in the Paper Sizes Chart lists all three units for every size in the A series, B series, and US group so you can copy the value your workflow expects without reaching for a calculator.
How to Look Up a Size and Get Its Pixel Count at Any DPI
- Open the Paper Sizes Chart and scan the reference table for the size you need in the A series, B series, or US group, with dimensions shown in millimetres, centimetres, and inches.
- In the converter panel, choose the same paper size from the dropdown to load its exact dimensions.
- Type the resolution you need into the DPI field. 300 is the standard for high-quality print, 72 is the classic screen value, and 150 is a common middle ground for office documents.
- Read off the pixel width and height that appear alongside the millimetre, centimetre, and inch values, then enter those numbers as your canvas size or export size.
The DPI calculation follows one rule: pixel size equals the dimension in inches multiplied by the DPI, rounded to the nearest whole pixel. Worked through end to end, an A4 sheet at 300 DPI comes out as 210 mm divided by 25.4 equals 8.2677 inches, times 300 equals 2480.31, which rounds to 2480 pixels wide. The height works the same way: 297 mm divided by 25.4 times 300 equals roughly 3507.87, which rounds to 3508 pixels tall. The same A4 at 72 DPI drops to about 595 by 842 pixels, which is roughly the size of a typical PDF page rendered on a 1x screen.
If your file is headed to a commercial print shop, ask what DPI they require before exporting. 300 DPI is the safe default for full-colour print, 150 DPI is usually fine for everyday office prints, and anything under 72 DPI tends to look soft on paper. If your output is a screen mockup or a web display, 72 to 144 DPI keeps the file light while still looking crisp at the intended zoom level.
A4 vs US Letter: The Near-Twin Sizes That Don't Quite Match
The single most common paper-size mix-up happens between A4 and US Letter. They look interchangeable but never quite line up. A4 is 210 by 297 millimetres, or 8.27 by 11.69 inches. US Letter is 215.9 by 279.4 millimetres, or 8.5 by 11 inches. A4 is 5.9 mm narrower and 17.6 mm taller than Letter, which is small enough to miss visually but big enough to matter on the printed page: a document designed for A4 will leave a horizontal white band when printed on Letter without margin scaling, and a Letter document printed on A4 will leave a vertical one. The fix is to pick the right size in your software's page settings before designing, not after.
The same near-match shows up between A3 and Tabloid. A3 is 297 by 420 mm, while Tabloid is 279.4 by 431.8 mm, so an A3 poster resized to Tabloid shifts about 17.6 mm narrower and 11.8 mm taller. Side by side, a complete paper size chart makes those differences obvious at a glance, which is why designers, print buyers, students, and developers keep one bookmarked: it stops the unit conversion, the system mismatch, and the resolution guesswork from slowing down the parts of the job that actually need attention.