If you're sending an A5 card, choosing the right envelope is essential for both presentation and postal compatibility. A5 cards are a popular format for greetings, invites and event stationery because they offer a balanced size — not too small, not too large — and give plenty of space for design and writing. But to post or gift it neatly, it needs to fit snugly inside the correct envelope size.
Getting the envelope right means your card will arrive in good condition, look well presented, and won’t incur unnecessary postage costs. Luckily, there’s a standard envelope size that matches A5 perfectly.
Best envelope size for A5 card
The best envelope size for an A5 card is C5. A C5 envelope measures 16.2 by 22.9 centimetres, or roughly 6.4 by 9 inches. This size is specifically designed to hold A5 paper or cards, which measure 14.8 by 21 centimetres. It offers just the right amount of space for the card to slide in easily while still holding it securely in place.
C5 envelopes are widely available in a range of finishes, colours and styles. Whether you want a plain white peel-and-seal for business use or a premium textured envelope for an occasion card, C5 gives you plenty of choice while staying standard in size.
Why C5 works best for A5
The reason C5 is the right fit comes down to how paper sizes are structured. A5 is exactly half the size of A4. C5 envelopes are designed to take an A4 sheet folded once, or an A5 sheet flat. This makes them perfect for A5 cards, invitations, or event flyers. The proportions ensure the card isn’t squeezed too tightly or moving around loosely inside the envelope.
If you're ordering custom A5 cards or printing your own, choosing a standard C5 envelope will keep things simple and avoid the need for custom envelope production or oversized postage.
Posting an A5 card in a C5 envelope
C5 envelopes generally qualify for standard letter postage with Royal Mail, as long as the envelope stays within the weight and thickness limits. If your card includes embellishments or is printed on very thick card stock, it’s worth weighing the finished item before posting. Adding inserts, multiple pages, or decorative elements may shift it into large letter territory.
For important or valuable cards, you might consider padded or board-backed C5 envelopes for extra protection, especially if the card is being sent in the post rather than handed in person.
Summary
The best envelope size for an A5 card is C5, which measures 16.2 by 22.9 centimetres. It’s made to fit A5 paper or cards flat, providing a clean and secure fit for posting or presentation. Whether you’re sending invitations, greetings or printed materials, using a C5 envelope ensures the right balance of appearance, protection and postage efficiency.
