Envelope reference · ISO C family
C4 envelope size
A document envelope sized to hold an A4 sheet flat, without folding, while leaving practical insertion clearance around the page.
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C4 dimensions and paper fit
In landscape orientation, C4 measures 229 × 324 mm, or 9.02 × 12.76 inches. One or more A4 sheets at 210 × 297 mm, unfolded.
| Unit | Width | Height |
|---|---|---|
| Millimeters | 229 mm | 324 mm |
| Centimeters | 22.9 cm | 32.4 cm |
| Inches | 9.02 in | 12.76 in |
| Pixels at 300 DPI | 2705 px | 3827 px |
Insert & folding
What fits inside C4?
One or more A4 sheets at 210 × 297 mm, unfolded. No fold is required for A4. A3 can be folded once to A4 before insertion.
Comparison
How C4 differs from nearby envelopes
C4 is 19 mm wider and 27 mm taller than A4. It is substantially larger than C5 and is not the same as a North American 9 × 12 inch envelope.
Works well for
Common C4 uses
- Contracts sent flat
- Certificates
- A4 reports
- Presentation documents
Check before using
Where it can go wrong
- Postal pricing assumptions
- US 9 × 12 templates
- Artwork with no allowance for seams or flaps
Postal note
Dimensions do not determine postage by themselves.
Postage categories depend on thickness, weight, destination, and carrier rules. “C4” identifies dimensions, not a guaranteed letter-mail rate.
Historical measurement source
Based on the C-series envelope convention.
The official ISO page identifies ISO 269:1985 as withdrawn. Paper Size Lab cites it as the historical designation source, not as a current postal requirement.
View ISO 269:1985 statusQuestions people ask
C4 envelope FAQ
What size is a C4 envelope?
C4 measures 229 × 324 mm, or 9.02 × 12.76 inches.
What paper fits in a C4 envelope?
One or more A4 sheets at 210 × 297 mm, unfolded.
How should paper be folded for a C4 envelope?
No fold is required for A4. A3 can be folded once to A4 before insertion.
Does a C4 envelope qualify for standard postage?
Postage categories depend on thickness, weight, destination, and carrier rules. “C4” identifies dimensions, not a guaranteed letter-mail rate.