Free design proof on every custom order: no templates, no stock SKUs
C6 envelopes measure 114mm x 162mm (roughly 4.49" x 6.38"), the ISO "C series" size built to hold an A4 sheet folded in thirds, the same relationship a #10 envelope has to a U.S. letter page. It's also generously sized for a flat A5 card or invitation with no folding at all. Businesses and individuals corresponding internationally, or anyone working in metric paper sizes, use the C6 as the everyday equivalent of a North American #10.
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Most of the world outside North America mails on ISO paper sizes, A4 rather than the U.S. letter format, and envelopes for that system follow their own numbered scale headed by the letter C. The C6, at 114mm by 162mm, is the size built specifically to receive an A4 sheet folded into thirds, functioning as the international counterpart to a North American #10 envelope in both purpose and everyday role.
The proportions of the ISO system make the C6 more versatile than its single stated purpose suggests. Because ISO paper sizes are related by simple halving, an A4 sheet folds down to A5, and a C6 envelope happens to accommodate a flat A5 sheet or card just as comfortably as a folded A4 letter. That makes it a natural size for invitations, greeting cards and any printed piece designed at A5 or A6 that needs to travel flat rather than folded, in addition to its main job as a business correspondence envelope.
International trade correspondence, European subsidiaries of North American companies, businesses that mail regularly to European or international addresses, and anyone printing stationery meant to pair with A4 letterhead all have reason to stock C6 envelopes rather than a U.S.-standard size. It's worth noting that a C6 is measurably smaller than a #10, so any correspondence produced on U.S. letter paper needs a different fold pattern, or a different envelope, to travel comfortably inside one.
As with any envelope, the practical choices are the same regardless of size standard: whether the envelope needs a window for a visible address, what closure style suits the mailing volume (gummed flaps for smaller runs, self-seal for anything mailed in bulk), and what stock weight matches the contents. A slightly heavier or textured stock is a common upgrade for C6 envelopes carrying invitations or greeting cards, where the envelope itself is part of the recipient's first impression rather than purely functional packaging.
Envelope weight is doing two jobs: it decides how the piece feels when it arrives, and it decides whether the contents show through. A 24lb wove is the everyday business standard and hides a folded letter adequately. Step up to 28lb or 32lb where the contents are thicker, where a check or a dark-printed insert would otherwise ghost through, or where the envelope itself is meant to signal that something considered is inside.
Why can I see the contents through my envelopes? The stock is too light for what is inside. Either move up a weight or add a printed security tint to the interior.
The constraint that surprises people is that you cannot print wherever you like. Postal systems reserve areas of the face for the address block, the postmark and machine-readable barcodes, and artwork intruding on them can slow a mailing down or get it rejected. Everything else is available (the flap, the reverse, and the areas of the face outside those zones) which is why so much envelope design lives on the back.
Can I print across the whole front? No. The address block, postmark area and barcode zone have to stay clear. We will show those on your proof.
How the envelope is folded and glued determines what it is good at. A side-seam envelope has glue lines up both edges and lies flat and rigid, which is what business correspondence and machine insertion need. A diagonal-seam envelope folds from a single diamond blank with the seams meeting in the middle. Traditionally the more formal construction, and the one used for invitations and announcements.
Does the seam matter? For machine inserting, yes. Side seam feeds reliably. For a hand-addressed invitation, diagonal seam simply looks right.
Three closures, chosen against volume and by hand or by machine. Gummed flaps need moisture and are the cheapest. Fine for a machine, tedious by hand in quantity. Peel-and-seal has a release strip over a pressure adhesive and is far faster for hand assembly. Latex self-seal bonds only to itself, so envelopes can be stacked without sticking and closed with a press.
Which for a hand-stuffed mailing? Peel and seal, without hesitation. The extra cost per envelope is recovered in the first hundred you do not have to lick.
At 114mm × 162mm this is the ISO C-series equivalent of the #10 relationship: it takes an A4 sheet folded twice into thirds. It also takes an A6 card unfolded, which is why it doubles as an invitation and greeting-card envelope throughout markets that use ISO paper sizes rather than US letter.
Is C6 the same as a #10? No. Similar purpose, different dimensions. If your mailing crosses between ISO and US letter markets, the two are not interchangeable and templates do not transfer.
Ask for samples before committing. Show-through and how a stock takes a fold are both impossible to judge on screen.
A return address and a logo, printed directly. It is the cheapest way to make mail look like it came from an organization rather than from a printer, and on a business envelope it is often all that is needed.
Photographic and full-bleed artwork. Worth noting that full-bleed coverage is only truly achievable on custom envelopes printed flat before converting. On a pre-made envelope the seams and flap edges limit how far ink can reach.
Metallic foil pressed into the stock, most often on the flap or as a monogram. On a textured or laid envelope the combination of foil against the ribbed surface is the traditional formal treatment.
A die-cut aperture backed with a clear film so an address prints once, on the letter, and shows through. It removes a whole addressing step from a mailing, which is why it dominates invoicing and statements.
Same family, genuinely different jobs. Your current selection is highlighted.
| Envelope | From | Format | Order it when |
|---|---|---|---|
| #10 Envelopes | $220 | 4.125″ × 9.5″, letter in thirds | Standard US business correspondence |
| #9 Envelopes | $220 | 3.875″ × 8.875″, nests in a #10 | A reply envelope goes in the mailing |
| 9 x 12 Envelopes | $240 | Holds letter size unfolded | The contents must not be folded |
| DL Envelopes | $190 | 110mm × 220mm, A4 in thirds | Letters and invoices on A4 |
| C6 Envelopes | $180 | 114mm × 162mm, A4 in thirds | Cards and shorter ISO correspondence |
| Custom Envelopes | $190 | Printed flat, converted to size | No stock size fits, or you want full bleed |
No. They serve a similar purpose in their respective paper systems but the dimensions differ, so window positions, inserting setups and artwork templates do not transfer between them. If a mailing crosses markets, treat them as separate jobs.
An A4 sheet folded twice into thirds, or an A6 card flat. That second use is why C6 doubles as the standard invitation and greeting-card envelope in ISO markets.
Yes, in the standard ISO window position. As with any window envelope, check it against your actual letter template. A designed layout frequently puts the address somewhere the standard aperture does not reach.
C6, generally, because its proportions suit cards and invitations while DL reads as business correspondence. For anything social or ceremonial, C6 is the safer choice.
Pricing for c6 envelopes starts at $180 and moves with quantity, size, material and finish rather than sitting on a fixed list. Setup is shared across the run, so the per-unit price drops steeply as the quantity rises: the gap between a few hundred and a few thousand is usually the significant one. Send the size, quantity and what it has to do and you get a firm figure back, not a range.
There is a practical minimum rather than a hard one. Every run carries artwork checks, a proof and a press setup, so a very small quantity of c6 envelopes prices poorly per unit even though we will still make it. If you are ordering a small batch, ask for pricing at two or three quantities at once: the curve usually shows that a modest increase costs very little more in total.
The clock starts when you approve the proof, not when the order is placed, which is the part most people are surprised by. You get a proof first: a digital proof showing the artwork with the clear zones and, where relevant, the window position marked. Nothing prints until you approve it. On a custom conversion the proof also shows the flat blank before folding. Turnaround after approval depends on the finish: anything laminated, foiled or die-cut adds a stage that cannot be compressed without causing problems later. Tell us the date you actually need them and we will work backwards from it rather than quoting a generic lead time.
Print-ready artwork with bleed and a safe margin, supplied as a PDF, AI or EPS. Photographic elements should be supplied at the resolution the finished size needs, not the resolution that looks sharp on screen. If your file is not print-ready, say so when you order. We would rather fix it before the proof than after the run.
Yes. ISO C6, A4 folded in thirds is the standard build, and the dimensions around it are yours to set. A size that sits efficiently on the press sheet often costs no more than a standard one, while an awkward proportion that wastes half the sheet does. Ask before you commit and we will tell you whether a small change to the dimensions saves a disproportionate amount.
In most cases they are the same product under a different name: the trade uses several terms for it depending on the region and the supplier. What actually defines this one is the build: 114mm × 162mm, a4 in thirds. Order it when cards and shorter ISO correspondence. If you have seen it called c6 envelopes printing elsewhere, describe what it has to do rather than which name you found, and we will match the specification.
Yes. We provide free samples, and on c6 envelopes it is worth asking for one, because the difference between white wove and white wove, heavy is obvious in the hand and invisible on a screen. Most orders run on white wove, but ask for whichever you are weighing up. You also get a free design proof before anything goes to press, so nothing is printed that you have not seen.
The usual choices are one or two color, full color, foil stamping. Finish is not decoration on this product so much as a decision about how long it survives and how it reads in the hand, so it is worth choosing against the job rather than the budget. Tell us where the finished piece ends up and we will say which finish is doing real work and which is only adding cost.
Yes, and that is what almost every order here is. Nothing in this catalogue is a stock item: c6 envelopes are manufactured to the specification you give us, with your artwork on them. Send your logo as vector artwork where you have it, since that scales to any size without softening. If all you have is a low-resolution file, tell us and we will say what it needs before it reaches the press.
Yes, and a repeat run is simpler than the first one. We keep your approved specification on file, so a reorder skips the setup decisions and goes straight to production. If nothing about the artwork or the specification has changed, there is nothing to re-approve. Tell us the previous order and we will match it rather than starting the specification again.
Yes. Regalo Print has been producing custom commercial print for businesses across the USA and Canada since 2008, and every order ships tracked. The tracking number reaches you the day the job leaves, not the day it arrives. If you are working to a fixed date, say so when you order so the production schedule is built around the delivery date rather than the other way round.
