C Envelope Paper Sizes

C0 917 × 1297 mm C1 648 × 917 mm C2 458 × 648 mm C3 324 × 458 mm C4 229 × 324 mm C5 162 × 229 mm C6 114 × 162 mm C7 81 × 114 mm C8 57 × 81 mm C9 40 × 57 mm C10 28 × 40 mm

Further Information

The dimensions of the C series sizes are defined by the ISO 269 paper size standard. The C series is most commonly used for envelopes. The area of C series paper is the geometric mean of the areas of the A and B series paper of the same number. For example, C4 has a bigger area than A4, but smaller area than B4. Therefore an A4 piece of paper will fit into a C4 envelope. The aspect ratio of C series envelopes is 1:√2, and this means that an A4 sheet of paper when folded in half, parallel to its smaller sides, will fit nicely into a C5 envelope. When it is folded twice, it will fit into a C6 envelope, and so on.

Format	Width × Height (mm)	Width × Height (in)
C0	917 × 1297 mm	36.1 × 51.1 in
C1	648 × 917 mm	25.5 × 36.1 in
C2	458 × 648 mm	18 × 25.5 in
C3	324 × 458 mm	12.8 × 18 in
C4	229 × 324 mm	9 × 12.8 in
C5	162 × 229 mm	6.4 × 9 in
C6	114 × 162 mm	4.5 × 6.4 in
C7	81 × 114 mm	3.2 × 4.5 in
C8	57 × 81 mm	2.2 × 3.2 in
C9	40 × 57 mm	1.6 × 2.2 in
C10	28 × 40 mm	1.1 × 1.6 in