C Envelope Paper Sizes

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 x Height (mm) Width x Height (in)
C0 917 x 1297 mm 36.1 x 51.1 in
C1 648 x 917 mm 25.5 x 36.1 in
C2 458 x 648 mm 18 x 25.5 in
C3 324 x 458 mm 12.8 x 18 in
C4 229 x 324 mm 9 x 12.8 in
C5 162 x 229 mm 6.4 x 9 in
C6 114 x 162 mm 4.5 x 6.4 in
C7 81 x 114 mm 3.2 x 4.5 in
C8 57 x 81 mm 2.2 x 3.2 in
C9 40 x 57 mm 1.6 x 2.2 in
C10 28 x 40 mm 1.1 x 1.6 in
C11 22 x 32 mm 0.9 x 1.3 in
C12 16 x 22 mm 0.6 x 0.9 in
C Paper Sizes C1 C2 C3 C4 C5 C6