Envelope sizes

A successful mailing depends on a large range of different factors, but for anyone who sends a package, letter, postcard, business cards, a gift or a dedication, their main objective is to ensure that the addressee opens what they have sent and gives it their attention.

Just as one takes pains with the smallest details of packaging for a gift to ensure that it looks attractive, a plain white envelope can convey formality and elegance. Sometimes, there is a lot more to getting it right than just sending postcards in a typical kraft-color envelope – sometimes, the envelope has to make the content seem attractive, even if it is just a white envelope containing an invoice for products or services.

Therefore, it is of fundamental importance to have a correct understanding of envelope sizes in order to properly make a request on our site for adjustment to your particular needs. Each size is appropriate for certain purposes, particularly in the business world. Some types of envelopes might seem like strange choices to the general public, but are in fact highly useful in certain specific business contexts.

In this guide, we offer you detailed explanations of envelope sizes, as well as informational graphics and tables that will help you to better understand the differences between models: from the standard or model envelope size to those with huge dimensions, passing through the popular American DL envelopes and many others along the way.

Take note of the instructions that we provide below, and make use of the tools that we provide you with. That's the only way you will find the best option for your particular situation! If you have any questions, remember that you have the customer service team at your disposal, to evaluate your situation and recommend the products that will best match your needs, whether for your home or your office.

Remember that one tool that is widely used by professionals to enhance their mailings is superimposed text. Our printers can print the logo of your company or personal brand on any of our envelopes or bags, so remember that you can request a quote customized to your needs without making any commitments.

TOOL 

To better understand the equivalencies here, you can consult the following informational graphic, where we show how medium-sized envelopes relate to small and large ones. For reference, note that C5 and C6 envelopes are considered medium-sized, whether they are plain white or coloured.

What is the standard size of an envelope?

For orientation purposes, it is useful to recall that C4 is the “folio” size envelope, C5 is the “quarto” size, and C6 is traditionally considered the standard letter size, although it is not the size most commonly used by businesses, as we will see.

The choice of the letter “C”, and its accompanying number, is not accidental. It follows the ISO 216 standard, which internationally standardized the classification of envelopes. The numbers are related to each other: they indicate that a given envelope is half the size of the one that precedes it. Thus, a C3 is half the size of a C2, a C4 is half the size of a C3, and so on.

Additionally, they have a direct correspondence with the dimensions of sheets of paper. To give a few examples: C3 envelopes, which are relatively large, are designed to hold DIN A3 sheets of paper; C5 envelopes are intended for the A5 paper size; and the relatively small C8 envelopes have ideal dimensions for inserting DIN A8 sheets of paper. You can check these and other details of this system in the following table.

Table of envelope dimensions from C0 to C10

Name	Size (mm)	Format equivalencies
C0	917 x 1,297 mm	A0 paper sheet
C1	648 x 917 mm	A1 paper sheet
C2	458 x 648 mm	A2 paper sheet
C3	324 x 458 mm	A3 paper sheet
C4	229 x 324 mm	A4 paper sheet. A3 sheet folded in half
C5	162 x 229 mm	A5 paper sheet. A4 sheet folded in half
C6	114 x 162 mm	A6 paper sheet. A4 sheet folded into 3 equal parts
C7	81 x 113 mm	A7 paper sheet. A5 sheet folded into 4 equal parts
C8	57 x 81 mm	A8 paper sheet
C9	40 x 57 mm	A9 paper sheet
C10	28 x 40 mm	A10 paper sheet

In addition to these sizes, there are other basic models that are not classified with the letter "C". These are shown in the following table, with a brief indication of their main (respective) uses. Also note that there are other, freer and more specialized options, such as the sizes used for invitation envelopes, which do not follow any fixed pattern or standard. Many of these are square-shaped envelopes, with all sides of equal length.

Name	Size (mm)	Format equivalencies
C5+	162 x 235 mm	A5 paper sheet. A4 sheet folded once
DL	110 x 220 mm	Similar to American envelopes. A4 sheet folded into 3 equal parts along the width side
DL+	114 x 229 mm	A4 sheet folded into thirds (“plus” format)
E4	280 x 400 mm	B4 paper sheet
B4	250 x 353 mm	Format for inserting a C4 envelope
B5	176 x 250 mm	Format for inserting a C5 envelope
B6	125 x 176 mm	Format for inserting a C6 envelope

If you'd like to go a bit deeper into the calculations used to arrive at all of these dimensions and proportions, you can take a look at this page, which covers further series such as B, commonly used for the production of books.

DL: American envelope size

Because of how important and established it is in today’s society, it is also necessary to mention another type of letter-sized envelope: DL. It is not equivalent to the aforementioned C6, as it is longer (on the lengthwise side) and of shorter height. Its dimensions are 220 x 110 mm. When we think of an “office” envelope, we generally think of this size. In other words, this type of envelope is designed to hold a DIN A4 sheet of paper, folded into three equal parts.

In terms of absolute numbers, the 220x110mm size is the one that we will have had by far the most contact with, since the communications that businesses send to our mailbox are in this format. These are envelopes used for sending invoices, welcome messages for new customers, and a great many more things.

It is a very common envelope size for companies like Correos, although each office of the state postal agency also offers C6 models for certain users, normally colored white, which tend to cost less than colored commercial envelopes.

Envelope formats for special uses

We not only work with the most common envelope formats, but also with models that, for whatever reason, are less common among the general public but are still highly useful. For example, there are envelopes with a window: a small opening that allows one to see part of an envelope's contents from the outside.

This feature is normally used with normal DL-sized envelopes: companies place headings on their letters that, when the letter is folded in a certain way, coincide with the aforementioned window and thus display the recipient's information (name, surname, street, postal code, etc.), thus removing the need to print this information a second time on the envelope itself, and the added costs that this would bring.

With a cardboard backing for certificates or diplomas, with a gusset for a wider opening so you can insert your hand, of the pocket type ... The catalogue at aploksnes.com offers a wide assortment of solutions, which can be brought to your door with a single click.

Some other models that are not directly related to envelope dimensions, and that are available on our website, are called opaque envelopes. This name refers to envelopes that are not transparent, even when held up to a light, whether for the purpose of having a more solid color, or because they have a special coating on the inside, or for some other reason.

Aside from the models mentioned above, it is possible that you will encounter a different envelope format, since there are many other classifications, not always related to the envelope dimensions: for example, they may have to do with special properties of the paper or the manufacturing material of the envelope, or with the manner of sending it.

Landscape orientation, with window, wallet type

Portrait orientation, with window, wallet type

Pocket type
Automatic closure, Gummed, and Self-adhesive

Portrait orientation, pocket type, with window

Landscape orientation, pocket type, with window

With gusset, pocket type
Expandable envelope for sending multiple sheets of paper

Envelope with cardboard backing, pocket type
Printed with the instructions “Please Do Not Bend” in English.
For programmes, certificates, diplomas

Other details besides the dimensions of an envelope: types of closure 

The closure of an envelope is another aspect of crucial importance when one is trying to choose one model or another. At aploksnes.com, we give it a great deal of attention. One of the most convenient options is self-adhesive closure: there is a small coating of adhesive material on the inside of the flap, so that, once the protective strip is removed, the flap can be securely affixed to the envelope, preventing it from opening up.

There are also envelopes with a string and washer, which are not very practical in the case of mass mailings, but can be very appropriate when one is sending a special, personalized letter to the recipient. The same applies to envelopes with a clasp, which are closed with a click.

One of the premium options are envelopes with magnetic closure: an interesting and sophisticated solution that allows an envelope to be opened and closed more than once, if needed. And the list goes on from there: envelopes with a lock, with a fold, gummed envelopes, etc. We have a great many options on our website.

• Gummed flap
• Self-adhesive
• Automatic closure
• Without adhesive
• Opening in the upper part
• String and washer
• Flap with fold
• Magnetic
• Clasp
• Lock

Envelope flaps: marking out differences

The flaps of envelopes are another detail that distinguishes the design and use of each model. The most common option, currently, is the wallet type, which has a small strip of paper to which the adhesive (or whatever other system of closure) is added. It is easy to open and close. Wallet-type flaps tend to be rectangular, though some models opt for a rounded shape.

A more traditional and vintage option is the so-called diamond style flap: the classic triangular flap of paper with a tip that, once the flap is closed, goes up to the halfway point of the envelope’s outer side.

Wallet-type, with rounded flap
Gummed, for use with certain postage machines.

Wallet-type, with rectangular flap
Gummed, for manual insertion

Wallet-type, with automatic closure
for manual insertion

Wallet-type, with trapezoidal flap
Gummed, for use with certain postage machines.

Angled, diamond-shaped flap
Banker-style envelope, gummed, for manual insertion

Flap for insertion
Gummed, envelopes for celebrations/events

Wallet-type envelope with self-adhesive flap
for manual insertion

The format of an envelope is everything ... almost

Now that you’ve been given an in-depth introduction to the different formats, you have probably realized that making a good selection of envelope is crucially important, not only from an aesthetic standpoint, but also because of the uses that each model is designed for. DL for mass mailings, C4 envelopes for inserting important documents on A4 sized paper, C7 envelopes for sending small cards with personal dedications ...

Besides the above, you need to keep other criteria in mind, such as the material, the color, whether the envelopes have windows or not, the positioning of the window, the type of envelope closure that is appropriate for the context of reception, and so on.

Whatever you are looking for, you can find it on our website: whether normal envelope sizes, or very large or small ones. Place your order online so that you’ll be able to send your post at the best price possible!