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    The ISO 216 paper size system is an international standard that is used in many places in the world in copy and print devices that defines paper sizes. Based on the metric system, the ISO paper size system uses a height-to-width ratio with an aspect ratio of 1 to 1.414 (The square root of 2). If a sheet is cut into two, the resulting halves are the same proportions as the original.

    The Standard for Series A, B and C Paper Sizes

    This standard defines three series of paper sizes; A, B and C. All successive paper sizes are derived from the base standard A0, which is a sheet of paper measuring 1 square meter or 841 x 1189mm. The most common size of paper is A4 (210x297mm), which is standard letterhead paper size. The C series of sizes is for envelopes, where the C4 (229 x 324mm) is defined under ISO 269 and is most often used with A4 size paper. The B series contains intermediate sizes for the A series but are sizes that are not frequently used.

    The United States and Canada do not widely use the ISO standard paper sizes. Instead, the United States uses the Letter, Legal and Executive system, and Canada uses a P-series of sizes. Unlike the international ISO 216 standard, these paper sizes are not based on a proportional aspect ratio system for size.

    American Standards

    The most commonly used sizes in U.S. office applications include the following, as defined by the American National Standard:

    • Letter: 216 W 279 mm
    • Legal: 216 W 356 mm
    • Executive: 190 W 254 mm
    • Ledger/Tabloid: 279 W 432 mm

    Canadian Standards

    The Canadian standard CAN 2-9.60M defines six formats;

    • P1: 560 W 860 mm
    • P2: 430 W 560 mm
    • P3: 280 W 430 mm
    • P4: 215 W 280 mm
    • P5: 140 W 215 mm
    • P6: 107 W 140 mm

    The Canadian P-series of paper sizes are the U.S. paper sizes rounded to metric dimensions. For example, the U.S. letter size is 216×279 mm mm compared to the Canadian P4 size which is 215×280 mm. The ISO 216 standard for this size would be the A4 with a size of 210x297mm.