The wrong envelope can bend a card, crowd a letter, or raise your postage. This standard envelope dimensions chart shows the main sizes in inches and mm.

It is built for US readers: office teams, wedding planners, and anyone who prints or mails. The most common US size is the #10 envelope (4 1/8 x 9 1/2 in). It fits a standard letter folded in thirds.

Standard Envelope Sizes Chart for the USA

Most standard envelope sizes fall into a few families. Each family has its own job.

Commercial envelopes are for letters, bills, and statements.

Size	Inches	mm	Typical use
#6 3/4	3 5/8 x 6 1/2	92.1 x 165.1	Small notes, receipts
Monarch (#7 3/4)	3 7/8 x 7 1/2	98.4 x 190.5	Personal letters
#9	3 7/8 x 8 7/8	98.4 x 225.4	Reply envelope inside a #10
#10	4 1/8 x 9 1/2	104.8 x 241.3	Standard business letter
#11	4 1/2 x 10 3/8	114.3 x 262.5	Thicker tri-folds
#12	4 3/4 x 11	120.7 x 279.4	Multi-sheet packets
#14	5 x 11 1/2	127 x 292.1	Legal-size papers, folded

A-series envelopes have a square flap. They suit cards and invitations.

Size	Inches	mm	Typical use
A2	4 3/8 x 5 3/4	111.1 x 146.1	Note cards
A6	4 3/4 x 6 1/2	120.7 x 165.1	4×6 photos, invites
A7	5 1/4 x 7 1/4	133.4 x 184.2	5×7 cards
A8	5 1/2 x 8 1/8	139.7 x 206.4	Larger greeting cards
A9	5 3/4 x 8 3/4	146.1 x 222.3	Oversized invitations
A10	6 x 9 1/2	152.4 x 241.3	Large cards

Large-format envelopes carry flat or lightly folded documents.

Size	Inches	mm	Type
6×9	6 x 9	152.4 x 228.6	Booklet
9×12	9 x 12	228.6 x 304.8	Booklet or catalog
10×13	10 x 13	254 x 330.2	Booklet or catalog
10×15	10 x 15	254 x 381	Catalog

Also know these types:

• Baronial envelopes: pointed flap, formal look. The 5 1/2-Bar matches the A2.
• Square envelopes: from 5×5 to 9 1/2 x 9 1/2 inches. They often cost extra to mail.
• Coin envelopes: the #1 coin is 2 1/4 x 3 1/2 inches. It holds keys, seeds, and small parts.
• Booklet envelopes: open on the long side, with side seams. Machines can insert into them.
• Catalog envelopes: open on the short side, with a center seam. They are stronger for heavy items, but you fill them by hand.

Envelope dimensions help you choose the right fit for letters and documents, but everyday packaging comes in many other shapes and sizes. If you’re comparing container measurements for storage, shipping, or everyday use, understanding standard soda can dimensions can give you another useful real-world size reference.

International Envelope Dimensions: A4, C5, C4, C6 & DL

A4 is a paper size, not an envelope size. It measures 210 x 297 mm under ISO 216. You pick an envelope by how you fold the sheet.

Envelope	mm	Inches	Fits A4 paper…
C4	229 x 324	9.0 x 12.8	Unfolded
C5	162 x 229	6.4 x 9.0	Folded once
C6	114 x 162	4.5 x 6.4	Folded twice
DL	110 x 220	4.33 x 8.66	Folded in thirds
B4	250 x 353	9.8 x 13.9	Large documents

Here is how these sizes line up with US ones:

• C4 is close to the US 9×12.
• C5 is close to the US 6×9.
• DL works like a slim #10.

Mailing abroad? Check the destination country’s postal rules first. Limits vary.

How to Pick the Right Envelope Size (Fit, Postage & Printing)

Start with the contents. Choose an envelope about 1/4 inch larger than the item on each side. That is enough room to slide it in. It is tight enough to stop the item from shifting.

Quick fit guide for 8.5 x 11 paper:

• Tri-folded: #10
• Half-folded: 6×9
• Flat: 9×12
• Check with stub: check envelope (3 7/8 x 8 7/8 in)

Cards and invitations:

• 4×6 photo: A6
• 5×7 card: A7
• RSVP card: A1
• Large invitation: A9 or A10

USPS letter vs flat.

Postage depends on size, thickness, and weight. Under USPS Domestic Mail Manual 201, a letter must meet these limits:

• Minimum: 3 1/2 x 5 inches, 0.007 inch thick
• Maximum: 6 1/8 x 11 1/2 inches, 0.25 inch thick
• Weight: up to 3.5 oz
• Aspect ratio (length divided by height): between 1.3 and 2.5

A square envelope has a ratio of 1.0. That makes it non-machinable, so it needs an added surcharge. Current prices are on the USPS prices page. As of July 2026, a one-ounce First-Class letter costs $0.82 with a Forever stamp. A one-ounce flat, such as a 9×12, costs $1.63. A 6×9 can go either way, depending on thickness and flexibility. Always confirm rates before a bulk mailing.

Printing on envelopes. Word and Google Docs need the right custom size:

• #10: enter 9.5 x 4.125 inches in landscape.
• 9×12: enter 12 x 9 inches.
• Paper weight: 24 lb feeds well in most laser and inkjet printers. 20 lb can jam in laser printers.
• Test first: print one envelope on plain paper before the full run.
• Window envelopes: do not print an address on the face. The window shows the address from the letter inside.

Eco options. Look for recycled paper, FSC-certified stock, or kraft envelopes.

Common mistakes:

• Choosing a tight fit that tears the flap.
• Using letter-rate stamps on a 9×12.
• Confusing A-series with baronial sizes of the same dimensions.

FAQs About Standard Envelope Dimensions

These are the quick answers people search for most.

What are standard envelope sizes?

The most common are #10, #9, A2, A6, A7, 6×9, and 9×12. The #10 (4 1/8 x 9 1/2 in) is the US business standard.

What are the dimensions of a standard DL envelope?

A DL envelope is 110 x 220 mm, or about 4.33 x 8.66 inches. It fits an A4 sheet folded in thirds.

What size envelope for 8.5 x 11 paper?

It depends on the fold. Use a #10 for a tri-fold, a 6×9 for a half-fold, and a 9×12 for a flat sheet.

Is 9×12 a standard envelope size?

Yes. It is a standard booklet and catalog size. It holds a flat 8.5 x 11 page, and it mails at the flat rate.

Is 5×7 a normal envelope size?

5×7 is a common card size. The matching envelope is the A7 at 5 1/4 x 7 1/4 inches.

Will a 5×7 card fit in an A7 envelope?

Yes. The A7 leaves about 1/4 inch of room around a 5×7 card. That makes it easy to insert.

Conclusion

Match the envelope to the contents, the postage class, and the print setup. Keep the key sizes in mind: #10, A7, 6×9, 9×12, and DL. Bookmark this envelope size chart for your next mailing.