When choosing the right envelope for your needs, understanding the wide range of envelope sizes is essential. Envelopes are designed to fit various printer paper sizes, which vary depending on regional standards. In this article, we’ll talk about the two primary systems and how these envelope sizes correspond to common paper sizes so that your documents can be properly folded, mailed, and presented.
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Definition: Envelope sizes
Envelope sizes refer to the standardized dimensions of envelopes, with each one designed to hold specific paper sizes, either flat or folded, so that documents fit securely without excessive movement or damage. The two primary systems are the ISO standard — used internationally — and the US standard, which follows different naming conventions and dimensions.
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International envelopes
International envelope sizes are standardized under ISO 269 and are designed to complement the A series. These corresponding envelopes autumn under the C series, where each envelope is sized to hold its same-numbered A-size paper without folding. This means that an A4 paper fits flat into a C4 envelope, a flat A5 paper into a C5 envelope, and so on. Additionally, the DL envelope (short for “Dimension Lengthwise”) is used for business letters and fits a tri-folded A4 paper.
Below, you can find the most common international envelope sizes.
| Envelope sizes | Dimensions (mm) | Fits paper size |
|---|---|---|
| C4 | 229 × 324 mm | A4 (flat) |
| C5 | 162 × 229 mm | A5 (flat) or half-folded A4 |
| C6 | 114 × 162 mm | A6 (flat), half-folded A5, or quarter-folded A4 |
| DL | 110 × 220 mm | Tri-folded A4 |
| C7 | 81 × 114 mm | A7 (flat) |
US envelopes
Standard US envelope sizes can be divided into several categories:
- Announcement envelopes
- Baronial envelopes
- Catalog envelopes
- Collection envelopes
- Coin & mini envelopes
- Commercial envelopes
- Square envelopes
- Window envelopes
While there are many more specialty and niche envelopes, this list includes the most common ones.
Announcement envelopes are also referred to as A-style envelopes, invitation envelopes, or social envelopes. They’re used for mailing announcements like invitations and greeting cards, but also for mailing photographs and personal stationery. They’re somewhat square-shaped, and, because they’re often used for personal or creative correspondence, they come in a wide array of colors.
The most popular announcement envelope sizes are Lady Grey (A-2) and Diplomat (A-9).
| Envelope sizes | Dimensions (inches) |
|---|---|
| A-2 (Lady Grey) | 4-⅜ × 5-¾ |
| 4-¾ × 6-½ | |
| A-7 (Besselheim) | 5-¼ × 7-¼ |
| A-8 (Carr's) | 5-½ × 8-⅛ |
| A-9 (Diplomat) | 5-¾ × 8-¾ |
| A-10 (Willow) | 6 × 9-½ |
Baronial envelopes are used for formal invitations and correspondence and are taller and narrower than A-style envelopes. They have a deep, pointed flap, which aids their classic and elegant appearance.
| Envelope sizes | Dimensions (inches) |
|---|---|
| 4 Baronial | 3⅝ × 5⅛ |
| 5-½ Baronial | 4⅜ × 5¾ |
| 6 Baronial | 4¾ × 6½ |
| Lee | 5¼ × 7¼ |
Catalog envelopes can also be called promotional envelopes and are rather big envelopes for mailing thick booklets, brochures, documents, and magazines. They often have a center seam and a short-side opening (top flap). Common sizes include 6 × 9, 9 × 12, and 10 × 13 inches.
Collection envelopes are a specific type of envelope that is typically used in nonprofit, religious, or fundraising contexts. They’re designed to make it easy for donors or members to contribute money, often in cash or check, during a collection period, such as a church service, school fundraiser, or donation campaign. Common sizes are based on commercial envelopes and include:
- #6¼ (3-½ × 6-¼ in)
- #6¾ (3-⅝ × 6-½ in)
- #9 (3-⅞ × 8-⅞ in)
Coin and mini envelopes are small-sized envelopes used for holding coins, jewellery, stamps, seeds, keys, and other tiny items. They’re also popular in crafts and gift packaging. Common coin envelope sizes are:
- #1 (2-¼ × 3-½ in)
- #3 (2-½ × 4-¼ in)
- #5 (2-⅞ × 5-¼ in)
- #7 (3-½ × 6-½ in)
Commercial envelopes, also known as business envelopes or office envelopes, have a long rectangular shape with a commercial-style flap, which is usually pointed or square. They’re used for business correspondence, such as invoices, letters, and statements. Their colors are typically white or off-white, but they can also come in vibrant colors to stand out or to match company colors.
The most popular commercial envelope size is #10 since it can hold a tri-folded Letter-size paper or a Legal-size paper folded into quarters lengthwise.
| Envelope sizes | Dimensions (inches) |
|---|---|
| #5 | 3-⅛ × 5-½ |
| #6¼ | 3-½ × 6 |
| #6¾ | 3-⅝ × 6-½ |
| #7 | 3-¾ × 6-¾ |
| #7½ | 3-15⁄16 × 7-½ |
| #8⅝ | 3-⅝ × 8-⅝ |
| #9 | 3-⅞ × 8-⅞ |
| #10 | 4-⅛ × 9-½ |
| #11 | 4-½ × 10-⅜ |
| #12 | 4-¾ × 11 |
| #14 | 5 × 11-½ |
If you’d like to know more about paper folding, click on the button below.
Square envelopes have equal-length sides and are used for greeting cards, invitations, marketing materials, or creative designs. Due to their non-standard shape, they require extra postage from USPS. Common sizes include:
- 5 × 5.5 in
- 5 × 6.5 in
- 7 × 7 in
Window envelopes have a transparent panel made of plastic or glassine that reveals printed content inside, typically the recipient’s address. As such, they’re commonly used in invoicing, billing, payroll, and other business mail to save time and improve accuracy when it comes to addresses. They’re available in single-window and double-window formats. Common sizes are based on commercial envelopes and include:
- #9 window
- #10 window
- #6¾ window
Flap styles
Envelope flap styles refer to the shape and placement of the flap used to seal the envelope. Different styles serve different functional and aesthetic purposes, and they’re often chosen based on the formality or practicality of the mailing. The image below shows all flap styles.
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FAQs
Based on ISO sizes, common international envelopes include:
- C4 (A4 flat)
- C5 (A5 flat or A4 folded)
- C6 (A6 flat or A4 folded twice)
- DL (A4 folded in thirds)
The perfect envelope size for a flat A5 paper is C5 (162 × 229 mm).
A5 is a paper measuring 148 × 210 mm, while C5 is an envelope measuring 162 × 229 mm. This means that a flat A5 paper comfortably fits into a C5 envelope.
Common US envelope sizes include:
- #10 (business): 4-⅛ × 9-½ in
- #9 (return): 3-⅞ × 8-⅞ in
- #6¾ (personal & business): 3-⅝ × 6-½ in
- A-2 (cards): 4-⅜ × 5-¾ in
