ISO Paper Sizes In the ISO paper size system, the height-to-width ratio of all pages is the square root of two (1.4142 : 1). In other words, the width and the height of a page relate to each other like the side and the diagonal of a square. This aspect ratio is especially convenient for a paper size. If you put two such pages next to each other, or equivalently cut one parallel to its shorter side into two equal pieces, then the resulting page will have again the same width/height ratio. The ISO paper sizes are based on the metric system. The square-root-of-two ratio does not permit both the height and width of the pages to be nicely rounded metric lengths. Therefore, the area of the pages has been defined to have round metric values. As paper is usually specified in g/m≤, this simplifies calculation of the mass of a document if the format and number of pages are known. ISO Sizes A series ISO Sizes B series ISO size variations The following sizes are all variations on paper sizes in the ISO series. Since these are european standards, the size in inches is aproxiamte. The current ISO 216 standard was introduced in 1975 and is a direct follow up to the german DIN 476 standard from 1922. The Netherlands have used the DIN/ISO standard since 1925, Belgium since 1924, England (UK) since 1959 and France since 1967. ISO 216 is also called EN 20216 in Europe.