/01 Every paper size in one place
What size is A4? How wide is Letter in millimetres? Which envelope fits a folded A4 sheet? These are the questions that interrupt print setup, design work, and document formatting all the time. This tool is a single reference for every standard paper size, shown in millimetres, inches, and points, so you check once and get back to work.
The reference covers the full range of standards: the ISO A, B, and C series used across most of the world, the North American sizes including Letter, Legal, Tabloid and the ANSI and Architectural series, plus the Japanese, Chinese, Swedish, French traditional, and imperial systems. Business card sizes are in here too, which matters because standard business cards differ between regions and getting it wrong means reprints.
Points matter more than people expect. PDF files and most layout software measure pages in points, with 72 points to the inch. When you are setting up a document by hand or writing code that generates one, the point dimensions are the ones you actually need.
/02 How the ISO A series works
The ISO A series has one clever rule at its heart. Every A size has the same proportions: one to the square root of two. That specific ratio has a special property. Fold a sheet in half and you get the next size down, exactly, with the same proportions. A0 folded once is A1, folded again is A2, and so on down to the A4 you put in your printer.
This is why scaling between ISO sizes never distorts a layout. A design that fits A4 enlarges perfectly to A3 or shrinks to A5 with no margins shifted and nothing cropped. It is also why the series feels so orderly: A0 is defined as one square metre of area, and every step halves it.
The B series sits between the A sizes for jobs that need something in between, and the C series is the envelope family. A C4 envelope takes an A4 sheet unfolded, C5 takes A4 folded once, and C6 takes it folded twice. Once you know the pattern, matching paper to envelope stops being a guess.
/03 A4, Letter, and the two-worlds problem
Most of the world uses the ISO system. North America uses Letter, Legal, and Tabloid instead, and the two systems do not agree. A4 is 210 by 297 millimetres. Letter is 216 by 279: a little wider and a little shorter. The difference sounds trivial until a document crosses between them, and then it is not.
A file designed for A4 printed on Letter loses the top and bottom margins, because the shorter page cuts into them. The reverse leaves ugly bands down the sides. Anyone who sends documents across that border, prints international forms, or prepares files for both markets learns to check the target paper size first.
The rule of thumb: A4 is taller and narrower, Letter is shorter and wider, and every layout that must work on both needs margins that survive either shape.
/04 Finding a size you cannot name
The tool does something a plain chart cannot: it works backwards. Search by name and it finds the size. Search by dimensions and it matches what you typed against every standard, returning the closest fits. Type a pixel count with a print resolution, such as a 300dpi scan, and it converts those pixels into physical dimensions and tells you which standard size that image would print at.
You can also upload an image or a PDF, and the tool reads its actual dimensions and finds the nearest matching paper size. That answers the question that comes up constantly when working from files rather than paper: what size is this thing, really, and what paper do I print it on?
Two sizes can also be compared directly, side by side, with an overlay view showing exactly how much bigger one is than the other. When the question is whether an A3 design fits a Tabloid sheet, seeing the two shapes laid over each other settles it in a second.
/05 A4 size in cm, mm, inches and pixels
A4 is 21 × 29.7cm, which is 210 × 297mm or 8.27 × 11.69 inches. It is the standard size for letters, forms, printer paper and documents in India, the UK, Europe and most of the world. In points, the unit PDF software uses, it is 595 × 842.
For on-screen and print design, the pixel size depends on resolution. At 300 pixels per inch, the usual target for good print quality, an A4 page is 2480 × 3508 pixels. At 150 ppi it is 1240 × 1754, and at the web's standard 96 pixels per inch it is 794 × 1123.
The neighbouring sizes follow from A4. A3 is double the area at 29.7 × 42cm, used for posters and drawings, and A5 is half at 14.8 × 21cm, used for notebooks and booklets.