Marketing Print
Envelope Sizes Explained — Which Envelope Fits Your Print Piece?
Choosing the right envelope is mostly about knowing what's going inside it. A letter folded in thirds, a flat brochure, a 5×7 invitation, a booklet — each needs a specific envelope size. This guide covers the most common envelope sizes, what fits inside each one, and how to pick the right envelope for business mail, marketing campaigns, and event invitations.
At a Glance
- Most common
- #10 (4⅛ × 9½") — standard business envelope for letters and tri-fold brochures
- For 5×7 cards
- A7 (5¼ × 7¼") — invitations, announcements, greeting cards
- For flat 8.5×11
- 9 × 12 catalog envelope — documents, presentations, unfolded flyers
- For 6×9 mailers
- 6½ × 9½ booklet envelope — postcards, half-fold brochures, small catalogs
- Clearance rule
- Envelope should be ¼" to ½" larger than the insert on each dimension
Common Envelope Sizes
Envelopes in the United States fall into a few naming conventions: numbered commercial envelopes (#10, #9, etc.), "A" series announcement envelopes (A2, A6, A7), and catalog/booklet envelopes described by their dimensions. Here are the sizes you're most likely to need.
Commercial Envelopes (Business Mail)
Commercial envelopes open on the long side. The flap runs along the top edge. They're the standard for business correspondence and direct mail.
The default business envelope. Fits an 8.5 × 11" letter folded in thirds, a standard tri-fold brochure, or a check. Used for invoices, statements, contracts, and virtually all routine business mail.
Slightly smaller than a #10 — designed to fit inside a #10 envelope as a return envelope. Commonly included in invoice mailings and donation appeals so the recipient can mail back a payment or form.
A compact envelope used for personal letters, remittance slips, and small enclosures. Fits a sheet of paper folded in quarters. Less common in business, but still widely used for payment envelopes and church offering envelopes.
Announcement Envelopes (Invitations & Cards)
"A" series envelopes are sized to hold cards and invitations. They're typically square-flap envelopes with a more formal look, and they're the standard for wedding invitations, event announcements, greeting cards, and thank-you notes.
Fits 4¼ × 5½" cards (quarter-fold from letter-size paper). Used for RSVP cards, thank-you notes, small announcements, and personal stationery.
Fits 4×6 postcards, photos, and invitations. A versatile mid-size option for event invitations and promotional mailers that are too large for A2 but smaller than 5×7.
The most popular invitation envelope. Fits a standard 5 × 7" card with enough clearance for easy insertion. The go-to for weddings, formal events, and premium announcements.
Fits 5½ × 8½" cards and half-fold invitations. Used when you need more space for inserts — an invitation plus an RSVP card plus a detail card, for example.
Catalog & Booklet Envelopes (Flat Inserts)
Catalog envelopes open on the short side (flap on the short edge), while booklet envelopes open on the long side. Both are used for mailing flat documents, booklets, and catalogs without folding.
Fits 6 × 9" booklets, half-fold brochures, and large postcards. A common choice for mailing small catalogs, programs, and multi-page documents that shouldn't be folded.
The standard flat-mail envelope. Fits 8.5 × 11" documents without folding — contracts, presentations, printed flyers, and reports. Also used for mailing booklets and magazines.
Extra clearance for thick document stacks, padded inserts, or 8.5 × 11" materials with a cover letter on top. Used when a standard 9 × 12 is too snug.
Which Envelope Fits Which Print Piece?
| Print piece | Size | Envelope |
|---|---|---|
| Letter (folded in thirds) | 8.5 × 11" → ~3.7 × 8.5" | #10 (4⅛ × 9½") |
| Tri-fold brochure | ~3.7 × 8.5" folded | #10 (4⅛ × 9½") |
| Half-fold brochure | 5.5 × 8.5" folded | 6½ × 9½" booklet |
| 5×7 invitation or card | 5 × 7" | A7 (5¼ × 7¼") |
| 4×6 postcard or photo | 4 × 6" | A6 (4¾ × 6½") |
| RSVP card or note card | 4.25 × 5.5" | A2 (4⅜ × 5¾") |
| Flyer or document (flat) | 8.5 × 11" | 9 × 12" catalog |
| Booklet or small catalog | 5.5 × 8.5" or 6 × 9" | 6½ × 9½" booklet |
| Legal documents (flat) | 8.5 × 14" | 10 × 15" catalog |
Choosing the Right Envelope for Your Job
Business correspondence
A #10 envelope handles the vast majority of business mail. If you're sending a letter, invoice, contract, or any standard document, fold it in thirds and use a #10. For a more professional appearance, consider custom-printed #10 envelopes with your company logo and return address — it makes your mail look intentional rather than generic.
Marketing mailers and direct mail
The envelope you choose affects open rates. A #10 blends in with standard mail, which can work for official-looking campaigns but may also get ignored. A 6×9 or 9×12 envelope stands out in a mailbox because it's a different shape and size from most bills and letters. Oversized envelopes tend to get opened more often — the trade-off is higher postage.
If you're mailing postcards or flat flyers, consider whether an envelope is even necessary. Postcards up to 6×11 can be mailed without an envelope at lower postage rates. See our postcard size guide and direct mail guide for more on mailing without envelopes.
Invitations and event announcements
The A7 envelope is the standard for 5×7 invitations — weddings, galas, fundraisers, and formal events. If your invitation suite includes multiple pieces (main invite, RSVP card, details card, map insert), check that everything fits before ordering envelopes. A thick stack may need an A9 or a slightly padded inner envelope.
For a polished look, consider matching the envelope color to your invitation design. Custom envelope printing — with a return address, monogram, or decorative flap — is common for formal events.
Flat documents and booklets
When a document shouldn't be folded — contracts, presentations, certificates, printed booklets — use a catalog or booklet envelope. A 9×12 catalog envelope is the standard for mailing 8.5×11 pages flat. For smaller booklets (like saddle-stitched programs or half-size catalogs), a 6½×9½ booklet envelope works well. See the booklet binding guide for help planning booklets.
Custom Envelope Printing
Printed envelopes elevate the look of any mailing. At minimum, printing your logo and return address on the envelope saves manual labeling and looks more professional. Beyond that, you can add color, taglines, or full-bleed designs to the front or back.
Common uses for custom-printed envelopes include:
- Business stationery sets — matching letterhead, business cards, and envelopes
- Invoice and billing envelopes — branded #10 envelopes with a return address window
- Marketing mailers — teaser copy on the outside to increase open rates
- Event invitations — printed return address with matching color or monogram
Postage Considerations
Envelope size directly affects postage cost. USPS rates are based on size, weight, thickness, and rigidity:
- Letters: Envelopes between 3.5×5" and 6.125×11.5", up to ¼" thick and 3.5 oz, qualify for the cheapest First-Class letter rate.
- Flats (large envelopes): Anything over 6.125×11.5" or thicker than ¼" mails as a "flat" at a higher rate. This includes 9×12 and 10×13 catalog envelopes.
- Square surcharge: Square envelopes (where the height-to-width ratio is less than 1.3) incur a USPS surcharge. Some A-series envelopes are close to square — check before printing a large run.
- Weight adds up: Multiple inserts, thick card stock, or heavy paper can push you into a higher weight bracket. Weigh a finished sample before committing to postage estimates.
Frequently Asked Questions
Need envelopes printed for a mailing, event, or your everyday business correspondence? Tell us the size and quantity and we'll get you a quote.