Singapore uses the ISO C series for envelopes: C4 at 229 x 324 mm takes an A4 sheet flat, C5 at 162 x 229 mm takes A4 folded once or A5 flat, and DL at 110 x 220 mm takes A4 folded in thirds. Our printed envelope templates cover these in four footprints, with or without a window: 108 x 222 mm (4.25 x 8.75 in), 162 x 229 mm C5 (6.38 x 9 in), 229 x 324 mm C4 (9 x 12.75 in), and a 114 x 241 mm pocket or wallet envelope (4.5 x 9.5 in). Pick the envelope from what goes inside it and how it is folded, then choose window or plain.
By Chris Tan, Marketing Manager, Alibaba Printing. Updated October 2026.
What are the standard envelope sizes in Singapore?
The ISO 269 C series, the same system used across Europe and most of Asia, because each C size is made to hold the matching A size paper. The three that cover almost every business job are C4, C5 and DL. C6 appears for greeting cards and small invitations, and C65 is an in-between size for A4 folded in thirds with a little more room than DL.
| Envelope | Millimetres | Inches | Holds | Typical use |
|---|---|---|---|---|
| C4 | 229 x 324 mm | 9.02 x 12.76 in | A4 flat, unfolded | Contracts, certificates, brochures, anything that must not be creased |
| C5 | 162 x 229 mm | 6.38 x 9.02 in | A4 folded once, or A5 flat | Letters with enclosures, invitations, catalogues |
| C65 | 114 x 229 mm | 4.49 x 9.02 in | A4 folded in thirds, with spare room | Letters with a card or cheque enclosed |
| DL | 110 x 220 mm | 4.33 x 8.66 in | A4 folded in thirds | Business letters, invoices, statements; the standard window envelope |
| C6 | 114 x 162 mm | 4.49 x 6.38 in | A4 folded twice, or A6 flat | Greeting cards, small invitations, RSVP cards |
Which envelope sizes do you print?
Four footprints, each available as a plain or window envelope, with print on the front and on the back flap. The templates are built in inches, so both measurements are given.
| Our template | Inches | Millimetres | Closest ISO size | Window option | Style |
|---|---|---|---|---|---|
| Letter envelope | 4.25 x 8.75 in | 108 x 222 mm | DL (110 x 220 mm) | Yes | Wallet, flap on the long edge |
| Pocket envelope | 4.5 x 9.5 in | 114 x 241 mm | Between DL and C65 | Yes | Pocket or wallet |
| C5 envelope | 6.38 x 9 in | 162 x 229 mm | C5 exactly | Yes | |
| C4 envelope | 9 x 12.75 in | 229 x 324 mm | C4 exactly | No |
White and coloured papers and parchment finishes are available; the options are on the envelope printing page. Letterheads and envelopes are usually printed together so the paper and colour match; see letterhead printing.
Which envelope fits A4 paper?
It depends on the fold. A4 flat needs C4. A4 folded once in half needs C5. A4 folded in thirds, the standard business letter fold, needs DL or our 108 x 222 mm letter envelope; use C65 or the 114 x 241 mm pocket envelope when a card, cheque or reply slip is enclosed with the letter and DL is too tight. A4 folded twice into quarters fits C6, though that fold suits cards better than letters.
What is the difference between a pocket and a wallet envelope?
The position of the flap. A pocket envelope opens on the short edge, so the flap is at the top of an upright envelope; it suits documents inserted flat and is the usual style for C4 and C5. A wallet envelope opens on the long edge, so the flap runs along the top of a landscape envelope; it suits letters and is the usual style for DL. Machine-inserted mail normally uses wallet envelopes. Either style can carry a window.
Where does the window go?
On a DL or letter envelope the address window sits on the front, lower left in most Singapore and European layouts, so that the address block on a tri-folded A4 letter shows through when the letter is folded with the address on the outer panel. The window is clear film, and the letter’s address block must be positioned to land behind it, which is why letterheads and envelopes are designed as a pair. Window envelopes save addressing time for invoices and statements; plain envelopes suit anything personal or confidential.
What should the artwork include?
Return address and logo on the front top left or on the back flap, with the right half of the front left clear for the recipient address and postage. Keep print at least 15 mm from the edges on the front and avoid the window area and the gum line on the flap. Supply artwork in CMYK at 300 dpi as a PDF built on the template for the chosen size; both front and back flap can be printed, and the paper colour affects how light inks appear, so dark or single-colour designs are safest on coloured and parchment stocks.
Envelope size: the quick decision rule
- A4 must stay flat: C4, 229 x 324 mm
- A4 folded once, A5 flat, invitations: C5, 162 x 229 mm
- Business letter, invoice, statement: DL or our 108 x 222 mm letter envelope, window if the address prints on the letter
- Letter plus a card, cheque or reply slip: 114 x 241 mm pocket envelope or C65
- Greeting card or RSVP: C6, 114 x 162 mm
- Match the letterhead paper and colour; order both together
Frequently asked questions about envelope sizes
What size envelope fits A4 paper in Singapore?
C4 at 229 x 324 mm for A4 flat, C5 at 162 x 229 mm for A4 folded once, and DL at 110 x 220 mm for A4 folded in thirds.
What is a DL envelope?
110 x 220 mm, the standard business letter envelope. It holds an A4 sheet folded in thirds and is the usual size for window envelopes.
What is the difference between C4 and C5?
C4 is 229 x 324 mm and holds A4 flat. C5 is 162 x 229 mm, half the area, and holds A4 folded once or A5 flat.
Can I print on both sides of an envelope?
Yes. The front and the back flap are both printable. Keep the recipient address area and the gum line on the flap clear of print.
Do you print window envelopes?
Yes, on the 108 x 222 mm letter envelope, the 114 x 241 mm pocket envelope and the C5. The C4 is plain.