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Our handy envelope size guide below will help you to work out which UK standard size envelope you'll need, plus hopefully give you a good understanding of envelope sizing for the future. Why not DOWNLOAD & PRINT our handy envelope size guide too. Pop it on your pinboard as an easy reference guide! CLICK HERE to open in a new window.


A standard DL envelope measures 110mm x 220mm. This is what most people consider a "letter envelope" and fits A4 paper folded into thirds. Business 'With Compliments' slips are designed to fit inside a DL envelope and usually measure 210mm x 99mm.
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A standard C3 envelope measures 458mm x 324mm. This is designed to fit unfolded A3 paper (which is double the size of A4 paper). Standard A3 paper size is 297mm x 420mm. 
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A standard C4 envelope measures 324mm x 229mm. This is designed to fit unfolded A4 paper. Standard A4 paper size is 210mm x 297mm.
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A standard C5 envelope measures 162mm x 229mm. This is designed to fit A4 paper folded in half, or A5 paper unfolded. Standard A5 paper size is 148mm x 210mm.

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A standard C6 size envelope measures 114mm x 162mm. This is designed to fit A4 paper folded into quarters, A5 paper folded in half or A6 paper unfolded (often the size of a flyer). Standard A6 paper size is 105mm x 148mm.

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Why not DOWNLOAD & PRINT our handy envelope size guide? CLICK HERE to open in a new window. Figured out which size envelope you need?
Head to our Shop by Size page to see the envelopes available.


  • Is there an easy way to work out which size envelope I need?

    A quick and easy way to remember which envelope size you need is to swap the "A" letter of your paper size for the letter "C". For example, if you want an envelope to fit an A4 sheet of paper, then you'll need a C4 envelope (and so on).

  • What size envelope do I need for an A4 brochure?

    An A4 paper or brochure (depending on the thickness of the brochure) will fit into a C4 size envelope, without having to hold the paper to fit.

  • What does the letter C mean in terms of envelope sizing?

    Paper comes in A and B sizes. C envelope size is the geometric mean of the A and B size of the same number. This calculation produces a size between the A and B dimensions to make an envelope to perfectly hold the A size paper. For example if you calculate the geometric mean of A4 and B4 paper this will give you the dimensions of a C4 envelope (which is the ideal size to hold an A4 sheet of paper unfolded).

  • Why do the 'C' numbers increase as the envelope sizes decrease? (e.g C4 is bigger than C5)

    This is because envelope sizing is based on the ISO paper size system, so a C5 envelope is designed to fit A5 paper and a C4 envelope is designed to fit A4 paper. The ISO standard paper sizing system works by using A0 size paper as the base point and largest size. The number next to the A specifies the number of folds in half needed from an A0. For example, A2 paper is A0 folded twice, A3 paper is A0 folded 3 times, A4 paper is A0 folded 4 times. Therefore the number increases as it relates to the number of folds.

  • What is a DL envelope? And what does DL stand for?

    The DL envelope originated in Germany in the 1920's and was then known as DIN Lang, however these days DL is known to stand for 'Dimension Lengthwise'.  A DL envelope is designed to fit an A4 piece of paper, folded into thirds.  This is one of the most common envelope sizes for business letters and you will find the majority of your standard post arrives in a DL size envelope. 




Envelope Size Dimensions (mm) To Fit
DL 110 x 220mm A4 folded in thirds, DL flyers, Comp slips
DL+ 114 x 229mm Bulky A4 papers folded in thirds
C6 114 x 162mm A6 size paper, C6 greeting cards, postcards
C5 162 x 229mm A5 size paper, A4 paper folded in half
C4 229 x 324mm A4 size paper
C3  324 x 458mm A3 size paper

Envelope Sizes - Signed, Sealed and Delivered Your Way Seal it your way with your choice of wallet envelopes or pocket envelopes that have the flap at the long or short edge. Whether you want to send photos, business letters, magazines, cards, invitations or literature; there are A4 and A5 envelopes to suit every occasion.

Post perfect with the right envelope sizes

Don’t pay more than you need to in postage by choosing the right envelope sizes for your needs. Whether you require business letters folded once or twice; there are C5, C6 and DL envelopes to suit your needs. You can find an envelope to keep your document intact with A5 or A4 envelopes.

Just some of the envelope sizes we stock include;

C4 Envelopes – A standard A4 envelope

C5 Envelopes – A standard A5 envelope

C6 Envelopes – An A5 envelope halved lengthways or
an A4 envelope folded twice

DL Envelopes – A4 envelope folded twice so it's a third the size of an A4 sheet

Whether you need coloured envelopes, black envelopes or different sizes of envelopes; wholesale purchasing can be tailored to your personal or business requirements. Whether you are looking for C5, C6, DL or A4 envelopes; we have high quality coloured envelopes, business envelopes and wholesale envelopes in envelope sizes to suit your needs.


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