Ed #12 Standards

Papers manufactured outside North America are typically produced using International Organization for Standardization (ISO) sizes. ISO sizes are based on a sheet of paper measuring one square meter, known as the AO size, although it is not one meter square. AO sheets measure 841 mm x 1189 mm (or 33.1” x 46.8”), a proportion, or aspect ratio, that is based on the square root of two. This ratio is used because a sheet with the aspect ratio of the square root of two can be divided parallel to its shortest side into two equal halves that will also have the aspect ratio of the square root of two. Successive papers in the series—A1, A2, A3, A4 and so on—are each half the size of the preceding paper size, measured by its shorter side.

Because the ISO sizes always have the same proportion, images can be scaled up or down to fit on different sizes of paper without cropping the image differently. An image on an A3 sheet, for example, can be scaled down to fit an A4 sheet. By the same token, brochures can be made by using the next larger size; for example, an A3 folded once will produce an A4 size brochure.

The most frequently used ISO paper size is the A4 size, which measures 210 mm x 297 mm (or 8.3” x 11.7”). There also are B standard sheets, which are used most frequently for posters and books, and C series papers that are only used for envelopes. (For a comparison of standard ANSI and ISO paper sizes, click here.)