What size envelope for A4?
A4 fits a C4 envelope flat, a C5 folded once, and a DL or C6/C5 folded in three.
Smallest envelope for each fold
A4 is 210 × 297 mm. The right envelope depends on how many times you want to fold it.
| Fold | Size of folded sheet | Smallest envelope | Envelope size | Spare (width, length) | Next sizes up |
|---|---|---|---|---|---|
| flat | 210 × 297 mm | C4 | 229 × 324 mm | 19 × 27 mm | - |
| folded in half | 210 × 148.5 mm | US A10 (Willow) | 152.4 × 241.3 mm | 3.9 × 31.3 mm | C5, C4 |
| folded in three (letter fold) | 210 × 99 mm | DL | 110 × 220 mm | 11 × 10 mm | US No. 10 (Business), C6/C5, US No. 11 |
| folded in quarters | 105 × 148.5 mm | C6 | 114 × 162 mm | 9 × 13.5 mm | US A6 (Thompson), DL, US A7 (Besselheim) |
At least 3 mm spare each way is required. Computed from the dimensions of ISO C and DL envelopes and the US sizes on the envelope sizes page.
Every envelope tested
Spare room in mm (width × length) for each fold; a dash means it does not fit.
| Envelope | Size (mm) | Flat | Half | Thirds | Quarters |
|---|---|---|---|---|---|
| DL | 110 × 220 | – | – | 11 × 10 | 5 × 72 |
| C6 | 114 × 162 | – | – | – | 9 × 14 |
| C6/C5 | 114 × 229 | – | – | 15 × 19 | 9 × 80 |
| C5 | 162 × 229 | – | 14 × 19 | 63 × 19 | 57 × 80 |
| C4 | 229 × 324 | 19 × 27 | 80 × 114 | 130 × 114 | 124 × 176 |
| US No. 7 3/4 (Monarch) | 98 × 190 | – | – | – | – |
| US No. 9 | 98 × 225 | – | – | – | – |
| US No. 10 (Business) | 105 × 241 | – | – | 6 × 31 | – |
| US No. 11 | 114 × 264 | – | – | 15 × 54 | 9 × 115 |
| US No. 12 | 121 × 279 | – | – | 22 × 69 | 16 × 131 |
| US No. 14 | 127 × 292 | – | – | 28 × 82 | 22 × 144 |
| US A2 (Lady Grey) | 111 × 146 | – | – | – | – |
| US A6 (Thompson) | 121 × 165 | – | – | – | 16 × 17 |
| US A7 (Besselheim) | 133 × 184 | – | – | – | 28 × 36 |
| US A8 (Carrs) | 140 × 206 | – | – | – | 35 × 58 |
| US A9 (Diplomat) | 146 × 222 | – | – | 47 × 12 | 41 × 74 |
| US A10 (Willow) | 152 × 241 | – | 4 × 31 | 53 × 31 | 47 × 93 |
Which one to pick
Use C4 when the document must stay flat: contracts, certificates, a stapled set of pages or anything with a card back. Use C5 for a few pages folded once; the fold goes across the middle so the sheet becomes A5. Use DL or C6/C5 for the standard letter fold: top third folded down, bottom third folded up. The C6/C5 gives 4 mm more width than DL, which makes pulling the letter out easier. See the single pages for C4, C5 and DL.
Frequently asked questions
What size envelope do I need for A4?
C4 (229 x 324 mm) for flat A4, C5 (162 x 229 mm) for A4 folded once, DL (110 x 220 mm) or C6/C5 (114 x 229 mm) for A4 folded in three.
Does A4 fit in a DL envelope?
Only if folded in three. The folded letter is 210 x 99 mm, with 10 mm and 11 mm spare.
Does A4 fit in a C5 envelope?
Folded once, yes. It becomes 148.5 x 210 mm, which leaves 13.5 mm and 19 mm spare.
What is the smallest envelope for a folded A4?
DL for a letter fold, C5 for a single fold, C6 for A4 folded in quarters.