The classic formats with examples of folding your A4 sheet

Thus for a sheet of paper in A4, A5, etc. corresponds an envelope in C4, C5... :

The C6 format (11.4 x 16.2 cm) for an A6 sheet (an A4 folded in four).
The DL format (11 x 22 cm) accommodates an A4 sheet folded in three in an accordion. This format is the most widely used in the world. It is also called C6/5. However, this format is being supplanted by the C5/6, which is slightly larger (114 x 229 mm) and is mainly intended for automatic insertion.
The C5 format (16.2 x 22.9 cm) is suitable for an A5 sheet (i.e. A4 folded in half).
The C4 format (22.9 x 32.4 cm) is designed to hold an A4 sheet (21 x 29.7 cm).
Sizes 24 (26 x 33 cm) or 26 (28 x 36.5 cm) for slightly thicker volumes.
The C4 (22.9 x 32.4 cm), 24 (26 x 33 cm) or 26 (28 x 36.5 cm) gusseted formats are intended for thicker volumes (catalogue files, etc.).

In addition to the above formats generally used in business correspondence, other intermediate formats are also available:

Do you want to make envelopes or pockets in a particular paper? in a particular format? for a particular window position?
Contact us without delay, we will study your needs together and offer you the solution best suited to your technical and budgetary constraints.