UK Envelope Sizes Reference
Choosing the right envelope means matching it to your paper size, checking it fits within Royal Mail size limits, and knowing which postage category it falls into. This reference covers all standard UK C-series envelopes, the popular DL format, and the Royal Mail dimensions and weight limits you need to know.
Standard C-Series Envelopes
The C-series (ISO 269) is designed so that each envelope holds the corresponding A-series paper unfolded. C5 holds A5 (or A4 folded in half), C6 holds A6 (or A4 folded in quarters), and so on.
| Envelope | Dimensions (mm) | Holds Paper Size | Paper Folding | Common Use |
|---|---|---|---|---|
| C3 | 458 × 324 | A3 flat | No folding | Large documents, posters, artwork |
| C4 | 324 × 229 | A4 flat | No folding | A4 documents, brochures, catalogues |
| C5 | 229 × 162 | A5 flat / A4 folded once | A4 in half | Greetings cards, invoices, half-fold letters |
| C5/6 (DL pocket) | 220 × 110 | A4 folded twice / A5 folded once | A4 in thirds | Standard business letters (same as DL) |
| DL | 220 × 110 | A4 folded twice / 1/3 A4 | A4 in thirds | Most common business envelope in the UK |
| C6 | 162 × 114 | A6 flat / A4 in quarters | A4 in quarters | Thank-you notes, RSVPs, small cards |
| C7 | 114 × 81 | A7 flat | A5 in quarters | Gift tags, miniature cards, seed packets |
Royal Mail Size & Weight Limits
| Category | Max Length | Max Width | Max Thickness | Max Weight | Fits Envelopes |
|---|---|---|---|---|---|
| Letter | 240 mm | 165 mm | 5 mm | 100 g | DL, C6, C7 |
| Large Letter | 353 mm | 250 mm | 25 mm | 750 g | C4, C5, DL (with contents) |
| Small Parcel | 450 mm | 350 mm | 160 mm | 2 kg | C3, padded envelopes |
Royal Mail minimum size for all mail: 100 × 70 mm. Items below this cannot be posted. Prices correct as of Royal Mail's current tariff — always check the Royal Mail website for the latest rates.
Postage Weight Steps
| Category | Weight Step 1 | Weight Step 2 | Weight Step 3 |
|---|---|---|---|
| Letter | 0–100 g | — | — |
| Large Letter | 0–100 g | 101–250 g | 251–750 g |
| Small Parcel | 0–1 kg | 1–2 kg | — |
Helpful Craft Tips
When making handmade cards, check whether your finished card (including embellishments) exceeds the 5 mm thickness limit for letters. Adding buttons, bows, or thick layered card can easily push it into the “large letter” postage bracket. Bulky cards in C5 or C6 envelopes may also need a “hand-stamp” surcharge if they can't go through the sorting machine.
Calculate Envelope Needs
Use our envelope calculator to find the right size for your project:
- Envelope Size Calculator — enter your paper or card dimensions to find the matching envelope and postage category
Envelope dimensions follow the ISO 269 standard. “DL” stands for “dimension lengthwise” and is technically a separate standard from C5/6, though the dimensions are identical. Royal Mail limits and prices are subject to change — verify at royalmail.com before posting.