ISO Envelope sizes
International standard ISO (International Organization for Standardization) 269 defines several standard envelope sizes, which are designed for use with ISO 216 standard paper sizes (the A series). The German standard DIN 678 defines a similar list of envelope formats.
This envelope series was designed to accommodate ISO A size papers. Metric measurements are the finished envelope size. Inch measurements are approximate (calculated at 25.4 mm = 1 inch and rounded off).
ISO Envelope Sizes
|Name||Size in millimeters||Size in inches||Usage and comments|
|C0||917 mm x 1297 mm||36.12 in x 51.6 in||For flat A0 sheet.|
|C1||648 mm x 917 mm||25.50 in x 36.12 in||For flat A1 sheet.|
|C2||458 mm x 648 mm||18 in x 25.50 in||For flat A2 sheet, A1 folded in half.|
|C3||324 mm x 458 mm||12.75 in x 18 in||For flat A3 sheet, A2 folded in half.|
|C4||229 mm x 324 mm||9 in x 12.75 in||For flat A4 sheet, A3 folded in half. Common.|
|C5||162 mm x 229 mm||6.38 in x 9 in||For flat A5 sheet, A4 folded in half. Common.|
|C6||114 mm x 162 mm||4.5 in x 6.38 in||For A5 folded in half. Common.|
|C7/6||81 mm x 162 mm||3.19 in x 6.38 in||For A5 sheet folded in thirds. Uncommon.|
|C7||81 mm x 114 mm||3.19 in x 4.5 in||For A5 folded in quarters. Uncommon.|
|DL||110 mm x 220 mm||4.32 in x 8.69 in||For A4 sheet folded in thirds, A5 in half. Common.|
Although DL is not part of the ISO C series, it is a very widely used standard size. DL, probably at one time the abbreviation of DIN Lang (Deutsche Industrie Norm, Long), is now identified as "Dimension Lengthwise" by ISO 269.