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.
C Paper Sizes Overview
| Format | Width × Height (mm)W × H (mm) | Width × Height (in)W × H (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 |
