Envelope · ISO C-series
C6 envelope
The C6 envelope is 162 × 114 mm — the standard size for greeting cards, invitations and short notes. It holds an A6 postcard flat, or an A4 letter folded into quarters. It is also the common "photo mailer" size for 4 × 6 inch prints.
Exact dimensions
C6 follows the C-series mathematics of ISO 269 (a standard since withdrawn by ISO, though its sizes remain the commercial norm): it is designed to hold an A6 sheet flat with a small clearance margin. Like all C-envelopes, it preserves the 1 : √2 proportion.
| Unit | Width | Height |
|---|---|---|
| Millimetres (mm) | 162 | 114 |
| Centimetres (cm) | 16.2 | 11.4 |
| Inches (in) | 6.378 | 4.488 |
C6 — 162 × 114 mm
Common contents
- · Greeting cards (birthday, holiday, thank-you)
- · Wedding RSVPs and small invitations
- · Photo prints in standard 4 × 6 inch size
- · Short personal letters
- · Save-the-date cards
Designing the front
Address blocks on C6 work best at around 60–70 mm wide and 35–45 mm tall, placed roughly in the lower-right third of the front. Stamps go in the top-right corner. Keep at least 10 mm clear of any edge to allow for postal sorting equipment to grip and read the envelope.
Printing & mailing notes
Card stock changes the rules slightly: a 300 gsm A6 card in a 100 gsm C6 envelope is stiff enough that some sorting machines route it as non-machinable — if a mailing matters, weigh and measure one finished piece at the post office before printing five hundred. Keep the bottom ~15 mm of the front clear for franking, stamp top-right, address block lower-right.
Frequently asked questions
What does C6 fit?
An A4 sheet folded in half twice fits (final size ~105 × 148 mm). An A6 sheet or postcard (105 × 148 mm) fits flat. Greeting cards, small invitations and short notes are typical contents.
How is C6 different from a postcard envelope?
C6 is the standard size used for postcard-style envelopes across Europe. Some manufacturers also call it a "postcard envelope" interchangeably. The dimensions are identical: 162 × 114 mm.
Is C6 acceptable for postal letter rates?
C6 is within the standard letter dimensions of most postal services, including Royal Mail, Deutsche Post, La Poste and Hellenic Post. Always check current local rules before bulk mailing — minimum thickness and weight rules can disqualify thin envelopes.
Are C6 envelopes good for printed photos?
Yes. A standard 4 × 6 inch photo (102 × 152 mm) fits with room to spare. Some specialty C6 envelopes are sold specifically as photo mailers, with a stiffener insert to prevent bending in transit.
What paper weight should I use?
90–120 gsm is typical for greeting-card C6 envelopes — slightly heavier than business envelopes, partly for feel and partly because card contents are denser than folded letters.
What is the difference between C6 and C6/C5?
C6 (162 × 114 mm) is the compact format — A6 flat or A4 folded twice. C6/C5 (229 × 114 mm) is the elongated hybrid that takes an A4 tri-fold like a DL but with C-series height. Same family, different fold.
Does a C6 envelope fit inside a C5?
Yes — the C-series nests by design, so a filled C6 (162 × 114) slips into a C5 (229 × 162). Wedding and event suites rely on this: the C6 RSVP envelope travels inside the C5 outer with the invitation.
What postage tier does C6 use?
Standard letter with most postal services — C6 sits comfortably inside typical small-letter dimension limits. Thickness is the usual trap: a card plus a stuffed C6 reply envelope can exceed the 5 mm letter band some posts enforce.