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.