Image & design · Print
Envelope size for your paper.
Pick the paper and how it is folded. The tool lists the ISO and North American envelopes it fits in, smallest first.
Inputs
Envelopes that fit
Pick a paper size.
What size envelope fits an A4 sheet?
ISO envelopes are designed around the A series. A C4 envelope (229 x 324 mm) takes an A4 sheet flat, a C5 envelope (162 x 229 mm) takes A4 folded once, and a DL envelope (110 x 220 mm) takes A4 folded twice into thirds. In North America a #10 envelope (4 1/8 x 9 1/2 in) takes a Letter sheet folded in thirds.
The tool folds your sheet, then checks it against each envelope in either orientation. An envelope counts as a fit when it is at least the spare-room setting larger than the folded paper in both directions. That setting (10 mm by default) is an assumption of this tool, not a standard: seams, flaps and thick paper all use up room, so test one first.
Frequently asked questions
What envelope fits A4 folded in three?
A DL envelope, 110 x 220 mm. An A4 sheet folded in thirds is 210 x 99 mm, which leaves 10 mm lengthwise and 11 mm across.
What envelope do I need for an A4 letter folded in half?
C5 (162 x 229 mm). A4 folded once is 210 x 148.5 mm.
What envelope fits Letter paper folded in thirds?
A #10 envelope (4 1/8 x 9 1/2 in, 104.8 x 241.3 mm) takes Letter folded in thirds (8.5 x 3.67 in) with room to spare. A #9 is a tighter fit and is included in the list when the room setting allows it.
Can A4 go in a #10 envelope?
Folded in thirds, A4 is 210 mm long and the #10 is 241.3 mm, so it fits in length; its 99 mm width fits inside 104.8 mm only with about 5.8 mm to spare, which is below the 10 mm default. Lower the setting to see it.
Why is the list different from a postal rule?
This is a fit check on paper and envelope dimensions only. Postage limits on size and weight are set by the carrier; check them separately.
Sources
Checked
- Markus Kuhn, University of Cambridge: International standard paper sizes (ISO 216 and ISO 269)
- Printer Working Group: PWG 5101.1-2023, Media Standardized Names v2.1 (North American, photo, envelope and card sizes)
ISO envelope sizes (C4, C5, C6, DL, B5, B4, C3) are from Kuhn / ISO 269; North American envelope sizes are from PWG 5101.1-2023. The 10 mm spare-room default is this tool's own assumption. Runs entirely in your browser. Nothing you type is sent or stored.
Scope
Sizes and results are arithmetic on published paper sizes and the numbers you enter. Printers and print shops set their own sizes, margins, bleed and resolution requirements, so confirm with yours before you print.