The A-series standard, which ranges from A0-A10, is based on a 1㎡ sheet (A0, full A sheet) with each successive size defined as half of the preceding size, dividing the sheet in the middle of the longer side. The ratio of the length of the short side to that of the long side is 1: √2.

The standard measurements for Japanese paper were established as part of the JES (Japanese Engineering Standards) in 1929. After World War II, these standard were maintained (with slight modifications) as the JIS (Japanese Industrial Standards), which became the present-day specification for “Writing paper and certain classes of printed matter—Trimmed sizes.”

The German standard for paper sizes was adopted for the A-series Japanese paper measurement standard. This German standard was originally established based on a proposal by the German scientist Friedrich Wilhelm Ostwald (1853-1932), and is now an ISO (International Organization for Standardization) standard.

When producing printed matter, it is necessary to print a crop mark to designate the edge of the finished product. For this reason, a separate size paper, known as a nobi (extended) size, is used, so that there is additional space beyond the crop mark. If one uses extended A3-size paper to print an A3-size document, for example, one is able to print it with the crop marks. Extended sizes vary depending on the paper manufacturer.