C1 Envelope Size
C1 measures 648 × 917 mm (25.51 × 36.10 in). The C series is used for envelopes.
| Millimetres | 648 × 917 mm |
|---|---|
| Centimetres | 64.8 × 91.7 cm |
| Inches | 25.51 × 36.10 in |
| Aspect ratio (long ÷ short) | 1.415 |
| Series | ISO 269 C series (envelopes) |
| Fits | An A1 sheet laid flat fits inside a C1 envelope |
| Fits inside | A C1 envelope fits inside a B1 envelope |
Where you will see C1
C1 is a very large envelope used for oversized documents and portfolios.
How C1 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 (594 × 841 mm for A1), so a flat A1 sheet fits inside a C1 envelope. The C1 envelope in turn fits inside a B1 envelope (707 × 1000 mm).
Frequently asked questions
What size is a C1 envelope?
A C1 envelope is 648 × 917 mm (25.51 × 36.10 inches).
What fits in a C1 envelope?
A flat A1 sheet (594 × 841 mm) fits in a C1 envelope with a small margin of 54 mm in width and 76 mm in height.
Related
- C0 Envelope Size917 × 1297 mm
- C2 Envelope Size458 × 648 mm
- A1 Paper Size594 × 841 mm
- B1 Paper Size707 × 1000 mm
Last updated: 2026-10-03