Envelopes are part of everyday business and personal stationery. They carry invoices, contracts, invitations and greeting cards. In the UK, envelope sizing can feel confusing because several naming systems are used at the same time. DL envelopes are common for letters, while the C‑series is based on standard A‑size paper.
This guide explains the most common envelope sizes and what they are used for. It also includes a quick envelope sizes chart to help you choose the right option for your documents, cards or invitations. If you are sending branded post, VistaPrint also offers custom envelope printing to match your stationery.
What are standard envelope sizes?
Below are the envelope sizes most commonly used in the UK. Each one fits a specific paper size or folding style.
DL envelope dimensions
Dimensions: 11 × 22 cm
- What fits: A4 folded into thirds
- Typical use: Everyday letters, invoices and statements
- Choose this size if: You are sending standard business correspondence or folded A4 documents
C4 envelope dimensions (A4 flat)
Dimensions: 22.9 × 32.4 cm
- What fits: A4 paper without folding
- Typical use: Contracts, certificates or formal documents
- Choose this size if: Your document must stay flat and uncreased
C5 envelope dimensions (A5 or A4 folded)
Dimensions: 16.2 × 22.9 cm
- What fits: A5 sheets or A4 folded in half
- Typical use: Brochures, letters with inserts, multi‑page documents
- Choose this size if: You want a professional envelope for folded A4 documents
C6 envelope dimensions (A6 cards and invitations)
Dimensions: 11.4 × 16.2 cm
- What fits: A6 cards or invitations
- Typical use: Greeting cards, party invitations, RSVP cards
Choose this size if: You are sending cards, thank‑you notes or small stationery
Envelope sizes chart
This envelope sizes chart provides a quick overview of common formats used in the UK.
| Envelope size | Dimensions (cm) | Fits paper/card size | Common uses |
| DL | 11 × 22 | A4 folded into thirds | Standard letters, invoices, everyday business post |
| C4 | 22.9 × 32.4 | A4 flat | Contracts, certificates, documents that should not be folded |
| C5 | 16.2 × 22.9 | A5 flat or A4 folded in half | Letters with inserts, brochures, multi‑page documents |
| C6 | 11.4 × 16.2 | A6 cards or invitations | Greeting cards, party invitations, RSVP cards |
| C6/5 | 11.4 × 22.9 | A4 folded in half lengthways | Slim inserts, folded letters, direct mail formats |
Envelope size guide: how to choose the right one
Choosing the correct envelope becomes easier when you follow a few simple steps.
1. Identify what you are sending
A single letter, several documents, a greeting card or a brochure may all require different sizes.
2. Decide if the paper should be flat or folded
Formal documents often stay flat, while letters are usually folded.
3. Check the final paper size
Measure the finished size after folding to ensure it fits comfortably.
4. Allow extra space for thickness
Multiple pages, inserts or card stock need additional room inside the envelope.
Common envelope sizes by use case
- Invoices and everyday letters: DL or C6/5
- Contracts and certificates: C4
- Flyers, booklets and folded letters: C5
- Invitations and thank‑you cards: C6
