Envelope Size Guide
Confused about envelope sizes? Well, keep reading to understand your C’s from your D’s… Check out our Envelope Size Guide in order of popularity to help you out with which envelopes are used for correspondence, sensitive documents, and more.

The envelope sizes that are getting the most attention
Envelopes continue to remain a popular stationery essential regardless of how fast the digital world progresses. The method of sending and receiving emails is more popular than ever nowadays. However, not all communication can be sent this way. Important documents, bills, cards and much more still need to be sent through the post office, and there are many of us who still prefer to communicate traditionally by using postal mail.
Confused about envelope sizes? Well, keep reading to understand your C’s from your D’s…
Check out our Envelope Size Guide in order of popularity to help you out with which envelopes are used for correspondence, sensitive documents, and more.
DL Envelope Size
The most popular size and considered a ‘letter envelope’ is ideal for everyday use. The DL envelope is 110 x 220mm, suitable for an A4 sheet folded twice or an A5 sheet folded once.
C4 Envelope Size
A C4 size envelope is often referred to as an A4 envelope as a piece of unfolded A4 paper fits perfectly. A piece of A3 paper also fits folded in half. These envelopes measure 324mm by 229mm. As this is a larger size it means that they can’t always be posted using regular postage stamps and would be classed as a ‘large letter’, meaning you would usually need to take them into a post office to be weighed and sent.
C5 Envelope Size
Another popular choice is the C5 envelope, it measures 162 x 299mm and is designed for sending unfolded A5 documents or folded A4 documents. The C5 is classed as a ‘letter’ for postage, so a standard postage stamp can be used.
C6 Envelope Size
The C6 size envelope is slightly taller but not as wide as the DL envelope. Measuring 114mm by 162mm in size it’s suitable for unfolded A6 or folded A5 documents, and A4 folded into quarters. As above, this type of envelope can usually be posted using a regular stamp.
C7 Envelope Size
The C7 is one of the least popular sizes of an envelope. Measuring approximately 83mm by 112mm, this envelope can fit a piece of A5 or A7 paper folded into four. The C7 small envelopes are generally used for RSVP cards or invitations. This small size envelope should only need a regular postage stamp.
C3 Envelope Size
The C3 envelope is designed for the larger A3 document. A standard C3 envelope measures approximately 324mm x 450mm which is ideal to enclose a piece of unfolded A3 paper perfectly.
Some of the less popular sizes of envelopes are:
- C8 57mm x 81mm - An A8 piece of unfolded paper will fit into a C8 envelope
- C9 40mm x 57mm - An unfolded piece of A9 paper will fit into a C9 envelope
- C10 28mm x 40mm - An A10 piece of unfolded paper will fit into a C10 envelope
Aston & James can provide you with all your envelope requirements.