International Envelope Sizes

The most common international envelope sizes are C4, C5, C6, DL, and B5. The C4 envelope is 229 x 324 mm, slightly smaller than an A4 sheet. The C5 envelope at 162 x 229 mm is an A4 sheet folded in half. At 114 x 162 mm, the C6 envelope is an A4 sheet folded into quarters. The DL (110 x 220 mm) is an A4 sheet folded into thirds widthwise. Finally, the B5 envelope at 176 x 250 mm is between the C5 and C4 in size. Other less common sizes include the C3, B4, B6, C7/C6, and C8/C7 which are generally just variations folded from standard A4/A5 sheets. The different sizes are useful for fitting varying content formats efficiently into mailing envelopes.