Updated July 2026
Envelope Size Calculator
Look up common envelope dimensions, compare A6, A7, #10, business, legal, and catalog envelopes, and check whether the size fits USPS letter or large envelope rules.
Check an envelope size
Use finished outside dimensions in inches.
Optional USPS mailing details
The default values work for a thin document envelope. Adjust these only if the envelope is thick, heavy, rigid, or stuffed.
Common envelope sizes
These are common commercial dimensions. USPS category depends on the final filled mailpiece.
| Envelope | Size | Common use | Mailing note |
|---|---|---|---|
| #10 Business Envelope | 9.5 x 4.125 in | Invoices, business letters, statements, and folded letter-size pages. | Usually letter-size when flexible and not over the letter thickness or weight limits. |
| #9 Reply Envelope | 8.875 x 3.875 in | Return envelopes, payment envelopes, and reply mail inserts. | Fits inside a #10 envelope and usually remains in letter-size dimensions. |
| #6 3/4 Envelope | 6.5 x 3.625 in | Personal letters, smaller notices, checks, and folded inserts. | Small but still within USPS letter-size dimensions. |
| A2 Envelope | 5.75 x 4.375 in | RSVP cards, thank-you notes, small invitations, and folded cards. | Letter-size by dimensions, but square-ish cards can need closer postage review. |
| A6 Envelope | 6.5 x 4.75 in | Greeting cards, invitations, announcements, and photo cards. | A common search size because it often sits between card stationery and mailable letters. |
| A7 Envelope | 7.25 x 5.25 in | 5 x 7 cards, invitations, announcements, and folded documents. | Letter-size by dimensions if flexible and thin enough. |
| A9 Envelope | 8.75 x 5.75 in | Half-fold cards, larger invitations, and document inserts. | Near the upper end of letter height, so thickness and rigidity matter. |
| 6 x 9 Booklet Envelope | 9 x 6 in | Small document packets, folded forms, and marketing inserts. | Often letter-size by dimensions, but document thickness can move it into flat handling. |
| 9 x 12 Catalog Envelope | 12 x 9 in | Unfolded letter-size pages, contracts, forms, and document packets. | Usually a USPS large envelope or flat by dimensions. |
| 10 x 13 Catalog Envelope | 13 x 10 in | Larger document packets, legal paperwork, and presentation materials. | Usually a USPS large envelope or flat when flexible and within thickness limits. |
| Legal-Size Document Envelope | 15 x 9.5 in | Unfolded legal-size pages, legal packets, and office documents. | At the USPS flat length limit, so do not exceed 15 inches on the long side. |
Find the size first
Use the size chart for quick lookups like envelope dimensions, business envelope size, A6 envelope size, A7 envelope size, and legal envelope size.
USPS letter vs flat
USPS letters must fit the letter length, height, and thickness window. Large envelopes or flats are bigger than letter size but still within flat maximums.
When the document is ready
After choosing the envelope, standardize the recipient address, compare postage, or send the document online if you do not want to print it yourself.
Envelope templates and printing
Envelope template searches usually mean you need a printable layout for the envelope size you picked. Match the template to the finished envelope dimensions, then check the physical envelope after printing because printer scaling can change the final placement.
Match the finished size
A #10 template should produce a 9.5 x 4.125 inch envelope layout. A7, A6, 9 x 12, and legal-size templates should match their final outside dimensions.
Keep the address clean
Format the address before printing so abbreviations, ZIP codes, apartment numbers, and line breaks are easy for USPS equipment to read.
Check the mailpiece
The template is only the layout. USPS classification depends on the final filled, sealed, measured envelope.
USPS size rules used by this calculator
Letter dimensions
USPS letter-size mail must be at least 5 inches long, 3.5 inches high, and 0.007 inch thick. It must be no more than 11.5 inches long, 6.125 inches high, and 0.25 inch thick.
Flat dimensions
USPS flats are larger than letter-size mail but no more than 15 inches long, 12 inches high, and 0.75 inch thick.
Source: USPS Postal Explorer letter and flat dimension rules. This tool does not quote postage prices because USPS rates can change.
Envelope size FAQ
What size is a #10 business envelope?
A standard #10 business envelope is 9.5 inches long by 4.125 inches high. It is commonly used for invoices, business letters, statements, and folded letter-size pages.
Is an A7 envelope a USPS letter or a flat?
An A7 envelope is commonly 7.25 x 5.25 inches, so it fits USPS letter dimensions if it is rectangular, flexible, thin enough, and not too heavy. Rigid cards, thick inserts, or unusual shapes can change handling.
What size is an A6 envelope?
An A6 envelope is commonly 6.5 x 4.75 inches. It is often used for greeting cards, invitations, announcements, and folded inserts.
What size envelope do I need for unfolded letter-size paper?
A 9 x 12 catalog envelope is the common choice for unfolded 8.5 x 11 inch paper. Because it exceeds the USPS letter-size maximum, it is generally treated as a large envelope or flat when it is flexible and within flat limits.
What is legal envelope size?
Legal envelope searches can mean different things. A legal-size document envelope for unfolded legal paper is often around 15 x 9.5 inches, while many legal offices also use #10 business envelopes for folded correspondence.
What makes an envelope a USPS flat?
A large envelope or flat exceeds at least one letter-size maximum but stays within the USPS flat maximums: 15 inches long, 12 inches high, and 3/4 inch thick.
Does envelope size change postage?
Yes. USPS pricing depends on mail class, shape, size, thickness, weight, and whether the piece is machinable. This tool classifies size and shape, then links to the postage calculator for live rate checks.
Can I print an envelope template and mail it?
Yes, if the finished envelope is rectangular, addressed correctly, sealed securely, and within USPS size and thickness rules. Always check the final physical envelope, not only the digital template dimensions.