Common UK Envelope Sizes Used in Printing

Envelopes can be very confusing. Paper has four main criteria namely size, weight, colour and finish but envelopes have all of these plus type, window position and nature of the sealing method. It is possible to print onto pre made envelopes but you can also print on a flat sheet of paper before converting it into a finished envelope.

Envelope Sizes

Like paper there is an internationally recognised ISO standard for envelope sizes that ‘dove tails’ with the A Series. The ‘A’ prefix is replaced by the ‘C’ prefix. The exception to this is the DL envelope which originates from the organisation responsible for standardisation across Germany – The German Institute for Standardisation (Deutsches Institute fur Normung – DIN). Back in 1922 the Institute introduced the A4 paper size that was later adopted by the ISO in 1975. The DL envelope, which is an abbreviation of DIN Lang, was designed to take a double folded A4 sheet and was so widely used that it was adopted by the Internal Standards Organisation even though it did not fit into the aspect ratio of the C series.


The C Series
C3 – 457 x 324mm
C4 – 324 x 229mm
C5 – 229 x 162mm
C6 – 114 x 162mm
DL – 110 x 210mm

Envelope Types

Banker – the traditional diamond flap envelope ideal for invitations and greetings cards


Wallet – opening on the long edge ideal for corporate letterheads

Pocket – opening on the short edge, most common on envelopes larger than DL


Window – a clear acetate that covers an aperture to reveal details e.g. name and address


Plain – an envelope that does not have a window


Board Back – a stiff board is used to provide protection and security for the contents from being bent or creased when in transit

Gusset – folded sides that can expand to accommodate bulkier items


Air Padded Bags – the body of the envelope is made from paper with a plastic lining comprising of small air pockets that provide protection and security to the contents. A popular brand is the Jiffy envelope.

Envelope-Types-Air Padded
Poly Bags – a clear polythene bag that is transparent to reveal the contents.


Envelope Sealing Methods

The three most common seals that you get on an envelope are:

Gummed – a small layer of dry adhesive that when moistened re-activates the glue for sticking. These where the first type of envelope to carry their own sealing mechanism and whilst not the most pleasant to use if licking yourself they are used for direct mail when using automatic enclosing machines. It is possible to steam open but generally speaking they are a relatively secure method of sealing an envelope. They can be stored for a relatively long time before the glue discolours or becomes un usable.

Self Seal – the most common envelope used today. Two layers of adhesive are used, one to each edge of the opening that when pressed together form an instant tight seal. They are quick and easy to use and although they can be re-opened, which could potentially be a security issue, they are economical and widely used. The seal strength can begin to weaken in a relatively short space of time so it is not recommended to store this type of envelope for more than 6 months.

Peal & Seal or Strip Seal – perhaps the easiest and quickest sealing method. A thin peel away strip of paper on the edge of the flap reveals a layer of adhesive that when pressed down forms an instant strong seal. These envelopes can be expensive but will store for a very long time without deteriation and once opened cannot be resealed making them very secure.

Envelope Dimensions

When quoting an envelopes dimensions you always give the edge with the flap on as the second dimension. The classic DL envelope therefore has a dimension of 110mm x 210mm when the flap is on the long edge. When using envelopes that have a window, the window size is quoted depth first (a) and length second (b). The most popular window size is 35 x 90mm but there are many sizes to choose from. The window position is quoted as the distance from the left hand edge of the envelope (c) and then the distance from the base of the envelope (d) with the flap at the top. The diagram opposite shows how this works in practice.


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