C3 Envelope Size
C3 measures 324 × 458 mm (12.76 × 18.03 in). The C series is used for envelopes.
| Millimetres | 324 × 458 mm |
|---|---|
| Centimetres | 32.4 × 45.8 cm |
| Inches | 12.76 × 18.03 in |
| Aspect ratio (long ÷ short) | 1.414 |
| Series | ISO 269 C series (envelopes) |
| Fits | An A3 sheet laid flat fits inside a C3 envelope |
| Fits inside | A C3 envelope fits inside a B3 envelope |
Where you will see C3
C3 is a large envelope that holds a flat A3 sheet, used for drawings and big documents.
How C3 relates to A and B sizes
In the ISO 269 C series, each C size is slightly larger than the A size with the same number (297 × 420 mm for A3), so a flat A3 sheet fits inside a C3 envelope. The C3 envelope in turn fits inside a B3 envelope (353 × 500 mm).
Frequently asked questions
What size is a C3 envelope?
A C3 envelope is 324 × 458 mm (12.76 × 18.03 inches).
What fits in a C3 envelope?
A flat A3 sheet (297 × 420 mm) fits in a C3 envelope with a small margin of 27 mm in width and 38 mm in height.
Related
- C2 Envelope Size458 × 648 mm
- C4 Envelope Size229 × 324 mm
- A3 Paper Size297 × 420 mm
- B3 Paper Size353 × 500 mm
Last updated: 2026-10-03