Quick answer: C4 envelopes measure 229 × 324 mm, or 22.9 × 32.4 cm and approximately 9.02 × 12.76 inches. A C4 envelope holds one A4 sheet flat without folding.
Measurement note: dimensions are stated width × height in portrait orientation. Turn the sheet through 90 degrees for landscape use. Millimetres are the controlling values for ISO sizes; inch figures are rounded conversions.
C4 dimensions
| Unit | Width | Height |
|---|---|---|
| Millimetres | 229 mm | 324 mm |
| Centimetres | 22.9 cm | 32.4 cm |
| Inches | 9.02 in | 12.76 in |
| Area | 74,196 mm² | 0.0742 m² |
What fits in a C4 envelope?
A C4 envelope holds one A4 sheet flat without folding. It can also hold smaller sheets, thin booklets or documents with modest clearance, but thickness must be tested.
Allow for thickness and clearance
The nominal relationship assumes ordinary sheets or cards. Multiple inserts, heavy card, folded booklets and mounted photographs add thickness and can make an envelope difficult to fill or seal. Test the complete assembled piece, not a single blank sheet.
Printing and addressing
Keep addresses, postage marks and barcodes clear of seams, windows and decorative backgrounds. Window envelopes require the address block in the document to align reliably after folding and inserting. For bulk mail, obtain the postal operator or fulfilment provider’s current artwork template.
Postal category
A familiar envelope designation does not guarantee a particular postal price. Weight, thickness and overall dimensions all matter. Royal Mail and USPS publish current limits; commercial mail can also have machinability and addressing rules.
C4 versus nearby envelopes
See the complete C-series guide for neighbouring dimensions. Choose the smallest envelope that accepts the finished contents without forcing, bowing or damaging corners. Excessively large envelopes can allow contents to move and may change the mailing category.
Frequently asked questions
What is C4 in inches?
C4 is approximately 9.02 × 12.76 inches. Use 229 × 324 mm for accurate purchasing and artwork.
Is C4 suitable for a card?
Yes, when the finished card is smaller than the envelope and its thickness allows easy insertion. A few millimetres of clearance on each side is normally desirable.
Does C4 have one fixed flap style?
No. Wallet, pocket, banker, peel-and-seal, gummed and window versions can share the same face dimensions. Flap and seam construction vary by product.
Test the complete mailed item
Postal success for C4 Envelope Size depends on the assembled item, not the nominal paper size. Build a dummy using the intended card, folds, inserts, adhesive and envelope. Weigh it, measure its maximum thickness without compressing it, and check whether embellishments create rigid or uneven areas. A piece that fits while empty may bow, split a seam or move into another price category once assembled.
Before producing a campaign quantity of C4 Envelope Size, take the finished dummy to the postal operator or mailing house. Bulk services can impose rules for address position, clear zones, barcodes, return addresses, tabs and machinability that do not apply to a single handwritten item.
Content and accessibility checks
On C4 Envelope Size, use a clear hierarchy for the recipient name, date, address, response deadline or call to action. Avoid placing essential information over folds, textured backgrounds or metallic finishes. Address panels should have strong contrast. A QR code should supplement, not replace, a readable URL or essential instruction; test it on the final printed stock under ordinary indoor light.
How to specify the size without ambiguity
For C4 Envelope Size, a reliable print specification states more than the familiar format name. Give the finished width and height, measurement unit, orientation, number of pages or panels, paper weight, surface, colour process, bleed, finishing and quantity. This prevents regional names and printer defaults from silently changing this particular job.
- Finished size: write width × height and identify portrait or landscape.
- Artwork size: distinguish the trimmed page from any larger bleed canvas or parent sheet.
- Stock: specify grammage or basis weight, coating, colour and recycled or certified requirements.
- Finishing: state folds, scoring, binding, drilling, corner rounding, lamination or mounting.
- Tolerance: ask the supplier what cutting, folding and registration variation should be expected.
When ordering C4 Envelope Size, a short name alone leaves important decisions unstated. A specification such as “finished size as stated above; portrait; 3 mm bleed; 170 gsm uncoated white stock; full colour both sides; scored where shown” is harder to misinterpret. When the format has regional variants, include the governing standard or exact dimensions every time.
Make a full-size physical proof
Screens do not communicate the physical scale of C4 Envelope Size reliably. Before a large order, print a representative page at 100%, trim it to the stated size and use it as the finished item will be used. Measure one horizontal and one vertical feature with a ruler. Fold it, place it in its envelope or holder where relevant, view it from the intended distance and ask someone unfamiliar with the design to find the main information.
A proof of C4 Envelope Size should check more than spelling. Look for text that is technically present but difficult to read, lines that sit too close to the trim, images whose important details enter a fold or binding area, barcodes or QR codes that do not scan, and stocks that crack or show through. For colour-critical work, a calibrated contract proof or press proof is more informative than an office print.
Sources and standards
The measurements and production guidance in this guide were checked against the following standards bodies, postal operators and print-platform specifications. Standards can be revised or withdrawn, so check the linked record when a contractual or regulated specification matters.