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Envelope Size Guide
Reference chart for standard envelope sizes.
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What this tool does
A reference chart of standard envelope sizes (DL, C4, C5, C6, US #10 and more) in millimetres and inches, showing which paper sizes each fits and how to fold to suit.
Reference
Standard envelope sizes
Envelopes run a few mm larger than the paper they hold for easy insertion.
| Envelope | mm | Inches | Fits |
|---|---|---|---|
| DL | 110 × 220 | 4.33 × 8.66 | A4 folded in three |
| C6 | 114 × 162 | 4.5 × 6.4 | A4 folded twice, or A6 card |
| C5 | 162 × 229 | 6.4 × 9 | A4 folded once, or A5 flat |
| C4 | 229 × 324 | 9 × 12.75 | A4 unfolded |
| US #10 | 105 × 241 | 4.125 × 9.5 | US Letter folded in three |
| A7 | 133 × 184 | 5.25 × 7.25 | Invitations, 5×7 cards |
| 6 × 9 | 152 × 229 | 6 × 9 | Letter folded once, small catalogues |
| 9 × 12 | 229 × 305 | 9 × 12 | US Letter unfolded |
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Match paper to the right envelope
Envelope sizing trips people up because the labels (DL, C5, #10) don't obviously map to paper. This guide lists the common envelope sizes in millimetres and inches and shows which paper size each one fits and how to fold it. Whether you're sending a letter, a card, or an unfolded document, you'll find the right envelope here.
The C-series and DL
European envelopes follow the C-series, designed around A-series paper. A C-size envelope holds the matching A-size sheet unfolded, or a larger sheet folded down. DL is the everyday business envelope sized for an A4 sheet folded in three.
- DL (110x220 mm) — A4 folded in three; standard business letters.
- C6 (114x162 mm) — A4 folded twice, or an A6 card.
- C5 (162x229 mm) — A4 folded once, or an A5 sheet flat.
- C4 (229x324 mm) — A4 unfolded; documents and brochures.
US envelope sizes
- #10 (4.125x9.5 in) — the standard US business envelope; Letter folded in three.
- A7 (5.25x7.25 in) — invitations and 5x7 cards.
- 6x9 in — documents folded once or small catalogues.
- 9x12 in — Letter-size documents unfolded.
How to use this guide
- Decide whether you'll send the paper flat or folded.
- Find the envelope that fits — flat needs a same-or-larger size, folded uses a smaller one.
- Follow the folding note (in three for DL/#10, in half for C5).
- Leave a few millimetres of clearance so the contents slide in easily.
Notes and limitations
- Envelopes are a touch larger than the paper they're named for, to allow easy insertion.
- Thick contents (several sheets or card) need a slightly larger envelope than a single sheet.
- Window envelopes have a fixed address position — check your letter's layout lines up before printing a batch.
FAQs
Quick answers
What envelope fits an A4 letter folded in three?
A DL envelope (110x220 mm), the standard business size. In the US, the equivalent is a #10 envelope for a Letter sheet folded in three.
Which envelope holds an A4 sheet unfolded?
A C4 envelope (229x324 mm). For US Letter unfolded, use a 9x12 inch envelope.
What is a C5 envelope for?
C5 (162x229 mm) holds an A4 sheet folded once in half, or an A5 sheet flat. It's common for thicker letters and small booklets.
Why is the envelope bigger than the paper?
Envelopes are sized a few millimetres larger than their nominal paper so the contents slide in and out easily. Thick contents may need the next size up.
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