Exploring C4: Envelope Size and Style Guide

The world of envelopes is vast and confusing – we’ve covered some of it on our Blue Summit Supplies blog, from business envelope dimensions to types of envelope seals. We even have some handy infographics to simplify your search for the perfect envelope. But beyond business envelopes and envelope seals, there is even more to know about envelopes.

Like sizing. 

Envelope Sizing Around the World

Envelope sizing is tricky because, as we mentioned before, it’s not globally standardized. Different parts of the world use different sizing for their envelopes and pages. In most of North America – the US, Canada, and some Latin American countries – we use named standard sizes for paper like Legal, Letter, Executive, and Tabloid.


North American Envelope Standards Infographic


North American Standard Paper Sizes
Paper Size Dimensions Typical Usage
Half Letter 8.5" x 5.5" Book pages, greeting cards, postcards
Letter 8.5" x 11" Letterheads, print & copy paper, notepads
Legal 8.5" x 14" Flyers, brochures
Ledger(also known as ledger or tabloid) 11" x 17"  Posters, magazines, publications

But we’re in the minority. Most of the world uses the ISO 216 and ISO 269 standard paper sizes, which are split into A, and B, whereas the C category denotes envelopes. A4 is the most commonly used paper size everywhere except for North America, where we don’t use the ISO 216 or ISO 269 as standard. A4 paper is comparable to our letter-size paper, though the dimensions are slightly different.

Here’s where the letters and numbers come in.

Instead of connoting sizes with names like Legal, Letter, etc. the ISO 216 & ISO 269 standards split paper and envelope sizes into alphanumeric identifiers – like A1, B2, C3. That’s why a C4 envelope size is different than a C5 envelope size even though their names are so similar. Each size has its own dimensions down to the tenth of an inch and are measured most commonly in millimeters. We’ve provided a handy paper types size chart to make it easier to understand ISO 216 & ISO 269 standard paper sizing.


ISO 216 Standards: A Series Sizes
Paper Size Dimensions
A0 841 mm × 1189 mm
A1 594 mm × 841 mm
A2 420 mm × 594 mm
A3 297 mm × 420 mm
A4 210 mm × 297 mm
A5 148 mm × 210 mm
A6 105 mm × 148 mm
A7 74 mm × 105 mm
A8 52 mm × 74 mm
A9 37 mm × 52 mm
A10 26 mm × 37 mm



ISO 216 Standards: B Series Sizes
Paper Size Dimensions
B0 1000 mm × 1414 mm
B1 707 mm × 1000 mm
B2 500 mm × 707 mm
B3 353 mm × 500 mm
B4 250 mm × 353 mm
B5 176 mm × 250 mm
B6 125 mm × 176 mm
B7 88 mm × 125 mm
B8 62 mm × 88 mm
B9 44 mm × 62 mm
B10 31 mm × 44 mm



ISO 269 Standards: C Series Sizes
Envelope Size Dimensions
C0 917 mm × 1297 mm
C1 648 mm × 917 mm
C2 458 mm × 648 mm
C3 324 mm × 458 mm
C4 229 mm × 324 mm
C5 162 mm × 229 mm
C6 114 mm × 162 mm
C7 81 mm × 114 mm
C8 57 mm × 81 mm
C9 40 mm × 57 mm
C10 28 mm × 40 mm


Examples of how ISO page sizes are used
Size Typical Usage
A0, A1 Technical drawings, posters
A2, A3 Drawings, diagrams, large tables
A4 Letters, Magazines, forms, catalogs, print & copy paper
A6 Postcards
A5, B5, A6, B6 Book pages
C4, C5, C6 Envelopes for A4 letters
(either unfolded, folded once, or folded twice, respectively)

For a more in-depth look into paper formatting and application, check out this resource.


Finding the Right Folded Fit

For US paper sizes, there are three main envelope categories: Commercial, Catalog, and Announcement. (There are also less commonly used styles of envelopes.) For business purposes, you will be using primarily commercial envelopes. These envelopes are long and slender. The most common type of commercial envelope size is the Number 10 envelope size since it fits folded Letter-size and Legal-size paper.

You can further break down your envelope needs depending on what sort of documents you’re mailing. There are simple gummed mail envelopes whose purpose is just to get its contents where it’s headed without any bells or whistles. Then there are windowed envelopeswhich take out the manpower or extra effort of addressing envelopes. A step further brings you to security envelopes, which are extra durable and tamper-proof to protect sensitive documents until they reach the intended recipient.

So how do you choose the right envelope?

Think about what you’ll be sending out. If it’s an advertisement or mailers, consider a blank envelope with a handwritten address for that extra personal touch. If it’s an invoice or other business correspondence, the address is likely printed straight on the document and a windowed envelope will save you time. Prepaid envelopes are also an option if you send out a high volume of mail.

As far as sizes, bigger is always better. The last thing you want is envelopes too narrow or shallow for your contents, so be thorough and make sure your paper and envelopes are complementary. But don’t go too big; a baronial envelope, for example, is overkill for sending a bill.

There are some envelope-paper combinations, like Letter and No. 10, that are tailor-made for one another. If you have a less standard paper size, however, a No. 10 envelope should still meet your needs if you’re willing to fold the contents. For more specialty concerns, like Quickbooks checks envelope sizes, check out our niche envelope resources.

We made the process of finding your perfect fit simple by creating an envelope size chart.


Envelope Size Chart

Envelope Dimension Size Chart


Moving Forward

Envelopes might not seem like the most exciting topic, mainly because they’re not. But they’re an integral part of business and by learning which envelopes best serve your needs, you’re investing in your organization and ensuring top-level professionalism.

What other details do you focus on to keep your business at its best? We want to know! Leave a comment or connect with us on social media, on TwitterFacebook, or Instagram.


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Grace Treutel is Blue Summit Supplies' Director of Culture. Currently she’s in training to become a Marriage & Family Therapist though her greatest love will always be the written word. Her three novel manuscripts have not yet been published - but just you wait. She lives in Huntsville with her  cute kids and cute pets.



Hi McKenna,

I would recommend placing your label in the center of your envelope, so that everything should have the same orientation as if it were written directly on the envelope. Hope this helps!

mckenna pierce

Hey Grace,

Thanks for this helpful article! I am using USPS Bulk Marketing Mail/ Permit Imprint to send out 10×13″ Envelopes. My design is on a 5″ × 3-1/2" sticker label that includes 1) paid postage in top right corner of label, 2) Return address in top left corner of label, and 3) Delivery address in center (slightly bottom portion) of label, all in a clearly legible format. Where do I place this on the 10″ × 13″ envelope? The USPS guidelines only specify that the delivery address be in the top portion of the envelope. Thanks!

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