How to use the chart
Choose a series (ISO A, ISO B, envelopes or North America) and a unit (millimeters, inches or points). Press a size name to see the same size in all three units, its area, and its size in pixels at 72, 96, 150, 300 or 600 dots per inch. That is the size to set for a design or a scan: for example A4 at 300 dpi is 2480 × 3508 pixels, and US Letter at 300 dpi is 2550 × 3300. If you have a measured sheet, type its width and height in millimeters to find the closest standard size.
How the sizes work
The ISO sizes used almost everywhere outside North America follow one idea: the height is the width times the square root of 2, so cutting a sheet in half across its long side gives two sheets of the next size, with the same proportions. A0 is one square meter, A1 is half of it, and A4, the common office size, is 210 × 297 mm. The B series is in between, with B0 one meter wide, and is used for posters and books. C sizes are envelopes made to hold A sizes, and DL holds an A4 sheet folded in three. In the US and Canada, Letter (8.5 × 11 in) and Legal (8.5 × 14 in) are used instead, with Tabloid (11 × 17 in) for large prints.
Questions
Why do some sizes show decimals? The North American sizes are defined in inches and converted exactly to millimeters (1 inch is 25.4 mm). What is a point? One point is 1/72 of an inch, the unit used by PDF files and print software. Why do pixel sizes depend on dpi? A pixel has no physical size, so dpi says how many pixels fit in an inch of paper. For printing graph paper at true size, try the Graph Paper Generator.