Envelope sizes chart
DL is 110 × 220 mm, C5 is 162 × 229 mm, C4 is 229 × 324 mm and the US No. 10 is 4 1/8 × 9 1/2 in.
ISO C series envelopes (C0 to C10)
The C series is the ISO 269 family of envelope sizes. Each C size is designed to hold the A size of the same number flat, with a few millimetres to spare. C0 is 917 × 1297 mm, the geometric mean of A0 and B0, and each size down is half the one before, like the A series. Wikipedia reports that ISO 269 was withdrawn in 2009 without replacement, but the sizes remain in universal use.
| Size | Millimetres | Centimetres | Inches | Holds |
|---|---|---|---|---|
| C0 | 917 × 1297 mm | 91.7 × 129.7 cm | 36.1 × 51.06 in | A0 flat |
| C1 | 648 × 917 mm | 64.8 × 91.7 cm | 25.51 × 36.1 in | A1 flat |
| C2 | 458 × 648 mm | 45.8 × 64.8 cm | 18.03 × 25.51 in | A2 flat |
| C3 | 324 × 458 mm | 32.4 × 45.8 cm | 12.76 × 18.03 in | A3 flat |
| C4 | 229 × 324 mm | 22.9 × 32.4 cm | 9.02 × 12.76 in | A4 flat (or A3 folded) |
| C5 | 162 × 229 mm | 16.2 × 22.9 cm | 6.38 × 9.02 in | A5 flat (or A4 folded once) |
| C6 | 114 × 162 mm | 11.4 × 16.2 cm | 4.49 × 6.38 in | A6 flat (or A5 folded) |
| C7 | 81 × 114 mm | 8.1 × 11.4 cm | 3.19 × 4.49 in | A7 flat |
| C8 | 57 × 81 mm | 5.7 × 8.1 cm | 2.24 × 3.19 in | A8 flat |
| C9 | 40 × 57 mm | 4 × 5.7 cm | 1.57 × 2.24 in | A9 flat |
| C10 | 28 × 40 mm | 2.8 × 4 cm | 1.1 × 1.57 in | A10 flat |
Common non-C envelopes
| Name | Millimetres | Centimetres | Inches | Holds |
|---|---|---|---|---|
| DL | 110 × 220 mm | 11 × 22 cm | 4.33 × 8.66 in | A4 folded in three, A5 folded in half lengthwise |
| C6/C5 (DL+) | 114 × 229 mm | 11.4 × 22.9 cm | 4.49 × 9.02 in | A4 folded in three |
| C7/C6 | 81 × 162 mm | 8.1 × 16.2 cm | 3.19 × 6.38 in | A5 folded in three |
| B6 | 125 × 176 mm | 12.5 × 17.6 cm | 4.92 × 6.93 in | C6 envelope, or a B6 sheet |
| B5 | 176 × 250 mm | 17.6 × 25 cm | 6.93 × 9.84 in | C5 envelope |
| B4 | 250 × 353 mm | 25 × 35.3 cm | 9.84 × 13.9 in | C4 envelope |
| E4 | 280 × 400 mm | 28 × 40 cm | 11.02 × 15.75 in | B4 sheet |
DL (DIN Lang) is the envelope for A4 folded into thirds. The “DL+” name for C6/C5 is a trade name, not a standard. B-series envelopes are made to hold the C envelope of the same number, for posting a smaller envelope inside a bigger one.
US envelope sizes
US envelope sizes are named by number or by “A” code (A2, A6, A7). The A codes are not related to the ISO A paper sizes, and are sometimes written A-2 for that reason.
| Name | Inches | Millimetres |
|---|---|---|
| No. 6 3/4 (Personal) | 3.625 × 6.5 in | 92.1 × 165.1 mm |
| No. 7 3/4 (Monarch) | 3.875 × 7.5 in | 98.4 × 190.5 mm |
| No. 9 | 3.875 × 8.875 in | 98.4 × 225.4 mm |
| No. 10 (Business) | 4.125 × 9.5 in | 104.8 × 241.3 mm |
| No. 11 | 4.5 × 10.375 in | 114.3 × 263.5 mm |
| No. 12 | 4.75 × 11 in | 120.6 × 279.4 mm |
| No. 14 | 5 × 11.5 in | 127 × 292.1 mm |
| A2 (Lady Grey) | 4.375 × 5.75 in | 111.1 × 146 mm |
| A6 (Thompson) | 4.75 × 6.5 in | 120.6 × 165.1 mm |
| A7 (Besselheim) | 5.25 × 7.25 in | 133.3 × 184.1 mm |
| A8 (Carrs) | 5.5 × 8.125 in | 139.7 × 206.4 mm |
| A9 (Diplomat) | 5.75 × 8.75 in | 146 × 222.2 mm |
| A10 (Willow) | 6 × 9.5 in | 152.4 × 241.3 mm |
The even-inch catalog and booklet sizes (6 × 9, 7 × 9, 9 × 12, 10 × 13 in) are also common. Source: Wikipedia's Envelope article, which lists the North American sizes; USPS limits from DMM 201.
Which envelope for which paper?
- A4: C4 flat, C5 folded once, DL or C6/C5 folded in three.
- A5: C5 flat, C6 folded once, DL folded in three.
- US Letter: No. 10 folded in three, 9 × 12 flat, A9 folded once.
The measurements for each fit are computed from the sheet and envelope dimensions on the page, with at least 3 mm to spare each way. Thick inserts need more room.
Frequently asked questions
What are the standard envelope sizes in the UK?
The most common are DL (110 x 220 mm), C5 (162 x 229 mm), C4 (229 x 324 mm) and C6 (114 x 162 mm), all from the ISO series.
What is the standard envelope size in the US?
The No. 10 business envelope, 4 1/8 x 9 1/2 inches (104.8 x 241.3 mm).
What size envelope fits an A4 letter folded in three?
A DL (110 x 220 mm) or C6/C5 (114 x 229 mm) envelope.
What size envelope fits A4 flat?
C4, 229 x 324 mm.
What envelope size is a greeting card?
An A6 card (105 x 148 mm) fits a C6 envelope (114 x 162 mm).
Is C4 bigger than C5?
Yes. C4 (229 x 324 mm) has twice the area of C5 (162 x 229 mm).