A Complete UK Guide to Envelope Sizes

Envelopes are essential for personal, professional, and creative correspondence. With so many sizes, styles, and materials available, choosing the right one can be overwhelming. This guide simplifies the process by explaining the most common envelope sizes used in the UK and their applications.

In the UK, envelope sizes are standardised according to the ISO 216 paper sizing system. This system's "C" series is used for envelopes and is designed to correspond with "A" series paper sizes. For example, an A4 sheet fits into a C4 envelope, while an A5 sheet fits into a C5 envelope.

Here’s a breakdown of the most popular sizes:

• C4 (324mm x 229mm): Ideal for sending unfolded A4 documents, such as business correspondence and reports.
• C5 (229mm x 162mm): Perfect for A5 documents or A4 sheets folded in half. It is often used for invitations and brochures.
• C6 (114mm x 162mm): Designed for A6 cards or A4 sheets folded into quarters, making it a popular choice for greeting cards and personal letters.
• DL (110mm x 220mm): Fits an A4 sheet folded into thirds and is widely used for business letters and promotional materials.
• C7 (81mm x 114mm): A compact size for A7 cards, frequently used for RSVP cards or small notes.

Consider these factors when selecting an envelope:

1. Purpose: The occasion—whether a formal business letter, a wedding invitation, or a greeting card—will influence your choice of size, style, and material.
2. Paper Size: Match the envelope to the paper or card inside. An A5 card, for instance, requires a C5 envelope.
3. Material and Weight: Heavier paper (e.g., 120gsm or 140gsm) offers a premium feel, while lighter paper (e.g., 100gsm) is more cost-effective for bulk mailings.
4. Colour and Finish: Choose a colour and finish that complements your contents. Ivory is elegant for wedding invitations, while bold colours make a statement.

Beyond standard sizes, specialty envelopes are available for unique needs:

• Square Envelopes: Popular for greeting cards and invitations, these are available in sizes from 130mm to 220mm square.
• Recycled Envelopes: Eco-friendly options made from post-consumer or pre-consumer waste, perfect for those prioritising sustainability.
• Peel & Seal Envelopes: Feature an adhesive strip for easy sealing, making them convenient for bulk mailings.
• Gummed Envelopes: Traditional envelopes with a moisture-activated adhesive, often used for personal letters.

• Business Use: DL and C4 envelopes are staples for sending invoices, contracts, and marketing materials.
• Personal Use: C6 envelopes are ideal for greeting cards, thank-you notes, and personal letters.
• Creative Projects: Coloured and square envelopes add flair to handmade cards, wedding stationery, and craft projects.

Q: What is the difference between C4 and C5 envelopes?

A: A C4 envelope fits an A4 sheet without folding, while a C5 envelope fits an A4 sheet folded in half.

Q: Can I use a DL envelope for A4 paper?

A: Yes, a DL envelope is designed to hold an A4 sheet folded into thirds.

Q: Are recycled envelopes durable?

A: Yes, high-quality recycled envelopes are just as durable as their non-recycled counterparts.

Q: What is the best envelope size for wedding invitations?

A: C5 and C6 envelopes are popular choices for wedding invitations, depending on the card size.

Q: How do I choose the right paper weight for envelopes?

A: For a premium feel, choose 120gsm or 140gsm paper. For cost-effective bulk mailings, 100gsm is a practical choice.

Understanding envelope sizes and their uses simplifies your decision, whether you're sending a business letter, a personal note, or a creative project. By considering the purpose, paper size, and material, you can select the perfect envelope for any occasion.