The A-Z of Envelope Sizes – Seven Different Types of Envelopes

image of one brown and one white envelope on top of a white table - Different envelope sizes

Believe it or not, the humble envelope has existed for over 4,000 years, beginning with Ancient Babylon. However, the first types of envelope were markedly different from those that are familiar to us today. Back then, what we might consider ‘letters’ were chiselled into stone tablets and then baked in a layer of clay. While we can only pity the postmen who had to lug these around and deliver the letters to the recipient, who would then smash the clay to read what was inside.

Around the same time, the Chinese were developing similar types of envelopes for their messages. As China spearheaded the development of paper, their letters were far less weighty and, instead, housed in clay spheres. Like their Babylonian counterparts, these would be broken, and the letter retrieved. However, around 200 BC, they replaced the clay with paper wraps, and something close to the envelope we use today was born.


image showing different sized and coloured envelopes - The A-Z of Envelope Sizes – Seven Different Types of Envelopes

The evolution of the envelope

Most of us are familiar with the idea of the sheets of paper, sealed with wax, that were used as envelopes during Medieval times. However, in the 19th Century, these paper packages started to evolve towards their more modern incarnation. The credit goes to British inventors Warren de la Rue, and Edwin Hill. After developing and patenting an envelope-making machine, the classic diamond design we use today began.


The importance of paper

Before we look at the different types of envelopes, their sizes, and uses, it’s worth knowing a little about how the paper they carry was developed. Rewind to 1786, when the idea of standardising the size of a letter was mooted, in a letter to the German scientist, Johann Beckmann, from his fellow countryman and physicist, Georg Christoph Lichtenberg. He proposed that the ratio between the length of a page and its width should be founded in the square root of two. In layperson’s terms, this is best described through the relationship between A4 and A3 papers. Because of the aspect ratio of a sheet of A3, if you cut it directly in half along its longer side, you’ll be left with two sheets of A4. Similarly, if you put two sheets of A4 side by side along their long edges, the combined measurements will create a sheet of A3.

This formula was adopted by the International Standardization Organization (ISO) and had a direct impact not only on the sizes of paper that we use but the types of envelope we use to house them in.


image showing layers of people on top of each other

A guide to envelope sizes

At first, choosing the correct envelope sizes for the right paper sizes can be confusing. With apparently random numbers and letters used to categorise paper and envelope sizes, there is more than a little room for error. However, the answers are a little simpler than you might first think.

Sheets of paper are categorised with the prefix, A, and B. No one knows why these letters have been chosen, but some thought suggests that using the first three letters of the alphabet is the easiest way to remember which size you’re dealing with. Each of the two letters refers to the aspect ratio of each sheet.


As easy as ABC

The largest size of A-series paper starts at A0, measuring one square metre. The next size down is A3, which is exactly half the size of A0. A4 is exactly half the size of A3, and so on, until you reach the smallest size, which is A10. A4 is the most commonly used size for copy and printer paper. However, this size is also the most popular for writing letters.

The B-series paper sizes follow the same principle: each sheet can be folded into two of the next size down. The numbers range from B0 to B10. Because B0 is larger than A0, B-series sheets tend to be larger than their A-sized counterparts, with the bigger sizes used for posters and notices.

Although still technically sheets of paper, envelopes are categorised by the prefix C. No one knows why. However, it’s logical to assume that because the base aspect ratio used to create the varying envelope sizes differs from A-series and B-series paper, the letter C should be next on the list.


image of a white envelope on a silver background - Different envelope sizes


Think of a number

Just as with different paper sizes, envelope dimensions are represented by numbers. Similarly, and possibly to keep everything on the right side of confusing, as those numbers increase in value, the envelope sizes decrease. In short, the bigger the number, the smaller the envelope,

which refers to the system developed by the International Standardization Organization, in which the measurements for envelopes are all created in relation to the baseline set by the largest size. Each subsequent size is exactly half the size of the one before. In addition, it’s worth knowing that the number associated with C-series envelopes corresponds directly with the size of the paper that will fit them. For example, if you’re looking to send an A7-sized sheet of paper or card, a C7 envelope will do the job. Should you want to send something weighing in at A3, a C3 envelope is what you’ll need.


close up image of beige envelopes - The A-Z of Envelope Sizes – Seven Different Types of Envelopes

What is a DL envelope?

However, there is an additional size to throw into the mix. Thankfully, this is one that most of us are familiar with. We tend to use the DL envelope to send standard letters. Unlike the A and B paper sizes, and the C envelope sizes, the D and the L do have a meaning beyond their places in the alphabet. ‘DL’ stands for ‘Dimensions Lengthwise.’ Created by the German branch of the ISO in the 190s, you’ll find these envelopes in offices, homes, and workplaces across the country. They house sheets of A4 paper and folded into three equal parts across their width, which has become the accepted way to send business and formal letters.

To help you make the right decision every time, here’s a handy envelope size chart, which lists the most popular envelope sizes and their dimensions and possible uses.


Our envelope size chart


Envelope Category Envelope Dimensions Typical Uses
DL envelope 110mm x 220mm The most common of all the envelope sizes, it is generally used for sending sheets of A4 folded into thirds.
DL+ envelope 114mm x 229mm While these are a little larger than standard DL envelopes, they’re typically used to send thicker sheets of A4 folded into thirds.
C7 envelope 84mm x 114mm An A7 envelope size, it’s used to send sheets of A7 paper, usually in the form of tickets, ID cards, and business cards.
C6 envelope 114mm x 162mm An A6 envelope size, these are typically used to send items such as flyers, small brochures, and postcards.
C5 envelope 162mm x 229mm An A5 envelope size, these are used to house flyers, booklets, and brochures.
C4 envelope 229mm x 324mm An A4 envelope size, these can be used to send sheets of A4 without folding them into thirds.
C3 envelope 324mm x 458mm The largest of the C-series envelopes, these are generally used to send presentation materials, posters, charts, and maps.


If you have someone in your office unfamiliar with the different envelope sizes you use, or you work from home and need to learn your way around, feel free to print out this envelope size chart. It’s also useful when choosing which envelopes you want to buy from our extensive range.


Types of envelope

However, knowing the envelope sizes is only half the battle. As you’ll see from our collection, there are various types of envelopes and learning a little about each can help you make the most of your mailing and keep your communications looking their best.

Typically made from paper, envelopes are measured in grammes per square metre (gsm), measuring their thickness and weight. As a rule of thumb, the greater the gsm, the thicker the paper is and the more premium it will look and feel. In addition, envelopes with a higher gsm will offer your letters, documents, posters, and flyers greater protection than those that register lower on the scale.


image of a coin on top of a white envelope - Envelope sizes


Standard or premium?

Standard envelopes, such as the Blake Purely Everyday Envelopes are ideal for sending letters and marketing materials in greater numbers. While they might weigh in at around 80gsm, they offer good levels of protection and are a cost-effective solution to mass mailing.

However, to ensure your letter makes an impression even before it’s opened, look for envelopes with a minimum gsm of 100. Envelopes such as the Blake Premium Business DL Envelopes offer 10gsm, quickly communicating that professional edge. In addition, envelopes such as these are much better suited to inkjet and laser printers so that every aspect of your mailing is crisp and clear. You’ll also find our range of business envelopes features those in different and subtle tones so that yours stands out from the crowd.


Outlook or windows?

One of the most popular types of envelope for business used to go under the name of the ‘outlook envelope,’ which most of us know better as the window envelope. At the very start of the 20th Century, these were invented by an American inventor, Americus F Callahan. He saw that those working for businesses and the telegraph service had to handwrite addresses on envelopes before sending them. While the typewriter was already in full swing, typing contact details on envelopes was even more difficult. His reasoning was to create an envelope in which the recipient’s address could be typed straight onto the letter but still be seen once inside. Early versions used rice paper over the window, which was transparent enough to keep the relevant information visible. A crystal-clear layer of plastic later replaced this.


a close up image of a red post box with the word, 'SAT' - Different envelope sizes


Over 100 years later, the principles of the window envelope remain the same. The recipient’s details can be printed straight onto the letter, which can be folded to allow them to be seen through the cellophane window. For businesses, this helps to speed up the process of addressing business communications while ensuring that the delivery details are always correct.

Like their standard counterparts, window envelopes are available in a range of gsm, from Blake Everyday Window Envelopes, which come in at 90gsm, to the more premium feel offered by the likes of the Blake Premium Pure Window Envelopes, which weigh in at 10gsm. Again, the choice comes down to a question of aesthetics, feel, and the level of protection offered.


Self-sealing envelopes

One of the most labour-saving additions to the envelope comes in the form of self-sealing strips. People of a certain age will remember the tongue-scraping effort in licking pre-gummed strips to seal the envelope shut. Self-sealing envelopes have replaced those with latex layers, forming an adhesive bond on contact with each other. Not only does this make the whole process much quicker and more effective, but in this post-pandemic era, it also helps to make it more hygienic, reducing the potential for spreading germs through saliva.

Our range of self-seal envelopes is available in a range of gsm, allowing you to choose the most appropriate for your letter or communication.


When you browse our collection of envelopes, you’ll see that a short product description accompanies each photo. These should tell you everything you need to know, from the gsm to the envelope sizes. You could receive your order as soon as the next working day with various delivery options available.

Share via
Copy link
Powered by Social Snap