Envelope sizes and what fits inside
The four envelopes you need most are C6 (114 × 162 mm), DL (110 × 220 mm), C5 (162 × 229 mm) and C4 (229 × 324 mm). An A4 sheet goes into C4 flat, into C5 folded once, into C6 folded twice and into DL folded in three.
Contents of this page
| Envelope | mm | Room (W × H) |
|---|
All envelope sizes at a glance
| Size | mm | Fits | Deutsche Post | Royal Mail |
|---|---|---|---|---|
| C7 | 81 × 114 | A7, small cards | Kompaktbrief | Letter (very small, so check the minimum size) |
| C6 | 114 × 162 | A6, A4 folded twice, A5 folded once | Standardbrief | Letter |
| DL | 110 × 220 | A4 folded in three, DL flyers | Standardbrief | Letter |
| C6/5 | 114 × 229 | A4 folded in three, with more room | Standardbrief | Letter |
| B6 | 125 × 176 | a C6 envelope, thick A6 cards | Standardbrief (right at the 125 mm limit) | Letter |
| C5 | 162 × 229 | A5, A4 folded once | Großbrief | Letter (just, 162 of 165 mm) |
| B5 | 176 × 250 | A5 booklets, a C5 envelope | Großbrief | Large Letter |
| C4 | 229 × 324 | A4 flat | Großbrief | Large Letter |
| B4 | 250 × 353 | thick A4 stacks, a C4 envelope | Großbrief or Maxibrief | Large Letter (at the maximum) |
| E4 | 280 × 400 | catalogues, documents in a folder | too large for a letter | parcel |
The postal columns assume the envelope stays within the weight and thickness limits of each service. A heavy C6 letter becomes a Kompaktbrief in Germany; a thick C4 envelope becomes a Maxibrief. Every limit for Germany is listed on German letter sizes, where you will also find the Royal Mail and USPS limits for comparison.
The logic behind the sizes
Envelope sizes follow the rule “A inside C inside B”. A sheet from the A series fits into the C envelope with the same number, and that envelope fits into the B envelope with the same number. If you want to include a reply envelope, for example, put a C5 envelope inside a B5 one.
DL and C6/5 sit outside this system. They are special sizes from DIN 678, made for the most common office case: an A4 letter folded in three.
Windowed or plain?
Window envelopes save you writing the address, but they need a letter with the address in exactly the right spot. On a DL envelope, the window under DIN 680 is usually 90 × 45 mm, 20 mm from the left and 15 mm from the bottom edge. How letterhead and envelope line up is explained on window envelopes.
Closures and paper
- Gummed: glue you moisten. Cheap, but tedious for larger quantities.
- Self-seal: adhesive on both flaps that sticks when pressed together.
- Peel and seal: an adhesive strip under a release liner. The most secure and today the most common.
Most envelopes are made from paper of 75 to 90 g/m². C4 and B4 often use 100 to 120 g/m² so they can hold a stack of paper safely. A printed inside pattern, usually blue or grey, stops anyone reading the contents against the light.
American envelope sizes
In North America, envelopes are numbered rather than named after paper sizes. The ones you are most likely to meet:
| Name | Inches | mm | For |
|---|---|---|---|
| No. 10 | 4.125 × 9.5 | 104.8 × 241.3 | Letter folded in three |
| No. 9 | 3.875 × 8.875 | 98.4 × 225.4 | reply envelope inside a No. 10 |
| A7 | 5.25 × 7.25 | 133.4 × 184.2 | 5 × 7 inch cards |
| A2 | 4.375 × 5.75 | 111.1 × 146.1 | Quarter Letter cards |
| 9 × 12 | 9 × 12 | 228.6 × 304.8 | Letter flat |
Do not confuse the American A7 and A2 envelopes with ISO paper sizes of the same name. They are completely different.
All pages about envelopes
- C3 envelopeA C3 envelope measures 324 × 458 mm and takes A3 flat. What fits, why it is too big to post as a letter and what to use instead.
- C4 envelopeA C4 envelope measures 229 × 324 mm and takes A4 flat. Types, window position, postage in the UK and Germany and how many sheets fit.
- C5 envelopeA C5 envelope measures 162 × 229 mm. What fits inside, why it is a Letter for Royal Mail but a Großbrief in Germany, and window positions.
- C6 envelopeA C6 envelope measures 114 × 162 mm. It fits A6 cards, A5 folded once and A4 folded twice, and goes as a standard letter.
- C7 envelopeA C7 envelope measures 81 × 114 mm. It fits A7 cards, business cards and vouchers, but is too small for most postal services.
- DL sizeA DL envelope is 110 × 220 mm and a DL flyer 99 × 210 mm. How an A4 sheet folds in, window position and print sizes with bleed.
- Window envelopesWhere the window sits on DL, C6/5, C5 and C4 envelopes, how a letter is folded to match it and why addresses sometimes slip out of view.
- German letter sizesStandardbrief, Kompaktbrief, Großbrief and Maxibrief explained in English: size limits, weights, 2026 postage and the changes announced for 2027.
- C seriesAll C sizes from C0 to C10 in mm and inches. Why A4 fits a C4 envelope, how the series is calculated and which standard covers it today.
- Envelope finderChoose your paper size and fold and get the envelopes that fit, with the spare room in millimetres. Works for A4, A5, A6, Letter and custom sizes.
Frequently asked questions
Which envelope fits A4?
Unfolded, C4. Folded once, C5. Folded twice crosswise, C6. Folded in three, DL or C6/5.
Which envelope fits A5?
C5 for flat A5 and C6 for A5 folded once.
Which envelope fits a postcard?
For A6 cards, a C6 envelope at 114 × 162 mm.
What is the difference between DL and C6/5?
C6/5 is slightly larger at 114 × 229 mm against 110 × 220 mm for DL. Both take an A4 sheet folded in three.
Is a C5 envelope a standard letter?
In Germany, no: C5 is 162 mm tall and the Standardbrief allows 125 mm. It goes as a Großbrief. Royal Mail accepts it as a Letter, because the limit there is 165 mm.