Envelope Sizes Guide
From business correspondence to wedding invitations, choosing the right envelope size ensures your documents fit perfectly. This comprehensive guide covers standard US envelope sizes, A-series, international formats, and specialty envelopes.
Envelope Size Finder
Find the right envelope for your document or card.
Standard Business Envelopes (Commercial)
The most common envelopes for business correspondence, invoices, and letters. #10 is the standard for most business mail.
| Name | Size (inches) | Size (mm) | Fits Document | Common Uses |
|---|---|---|---|---|
| #6¾ (Regular) | 3⅝" × 6½" | 92 × 165 mm | 3½" × 6" | Personal letters, checks |
| #7 (Monarch) | 3⅞" × 7½" | 98 × 191 mm | 3⅝" × 7¼" | Executive correspondence |
| #9 | 3⅞" × 8⅞" | 98 × 225 mm | 3⅝" × 8⅝" | Business reply mail |
| #10 (Standard) | 4⅛" × 9½" | 105 × 241 mm | 8½" × 11" folded in thirds | Standard business letters |
| #11 | 4½" × 10⅜" | 114 × 264 mm | 4¼" × 10" | Legal-size documents (folded) |
| #12 | 4¾" × 11" | 121 × 279 mm | 4½" × 10¾" | Large business documents |
| #14 | 5" × 11½" | 127 × 292 mm | 4¾" × 11¼" | Oversized business mail |
Business Envelope Tips:
- #10 is standard: Fits 8.5" × 11" letter folded in thirds
- Window envelopes: Available in #9, #10, #11 for showing address
- Security tint: Interior patterns prevent document visibility
- Self-seal: Peel-and-seal strip eliminates moisture
Announcement Envelopes (A-Series)
Square-flap envelopes designed for greeting cards, invitations, and announcements. The "A" designation indicates Announcement.
| Name | Size (inches) | Fits Card Size | Common Uses |
|---|---|---|---|
| A-1 | 3⅝" × 5⅛" | 3½" × 4⅞" | RSVP cards, place cards |
| A-2 | 4⅜" × 5¾" | 4¼" × 5½" | Thank you notes, small cards |
| A-4 | 4¼" × 6¼" | 4" × 6" | 4×6 photos, postcards |
| A-6 | 4¾" × 6½" | 4⅝" × 6¼" | Standard greeting cards |
| A-7 (5×7) | 5¼" × 7¼" | 5" × 7" | 5×7 invitations, photos |
| A-8 | 5½" × 8⅛" | 5¼" × 7⅞" | Large announcements |
| A-9 | 5¾" × 8¾" | 5½" × 8½" | Large greeting cards |
| A-10 | 6" × 9½" | 5¾" × 9¼" | Oversized announcements |
Announcement Envelope Features:
- Square flap: Elegant appearance for formal occasions
- Popular for weddings: A-7 is standard for wedding invitations
- Color options: Available in wide range of colors and textures
- Inner envelope: Often used with outer envelope for formal events
Catalog & Booklet Envelopes
Open-end (short side) envelopes designed for catalogs, magazines, and documents that shouldn't be folded. Side-seam construction for durability.
| Name | Size (inches) | Fits Document | Common Uses |
|---|---|---|---|
| 6" × 9" | 6" × 9" | 5¾" × 8¾" | Booklets, small catalogs |
| 6½" × 9½" | 6½" × 9½" | 6¼" × 9¼" | Brochures, newsletters |
| 9" × 12" | 9" × 12" | 8¾" × 11¾" | 8.5×11 documents flat |
| 10" × 13" | 10" × 13" | 9¾" × 12¾" | Magazines, legal documents |
| 11½" × 14½" | 11½" × 14½" | 11¼" × 14¼" | Legal-size documents flat |
| 12" × 15½" | 12" × 15½" | 11¾" × 15¼" | Large catalogs, posters |
Booklet Envelopes (Side Opening)
| Size | Dimensions | Fits | Uses |
|---|---|---|---|
| 6" × 9" | 6" × 9" | 5¾" × 8¾" | Half-page documents |
| 9" × 12" | 9" × 12" | 8¾" × 11¾" | Full letter-size flat |
| 10" × 15" | 10" × 15" | 9¾" × 14¾" | Legal documents, photos |
Square Envelopes
Perfect for wedding invitations, special announcements, and creating a distinctive look. Note: Square envelopes require additional postage.
| Size | Dimensions | Fits Card | Postage Note |
|---|---|---|---|
| 5" Square | 5" × 5" | 4¾" × 4¾" | Non-machinable surcharge |
| 5½" Square | 5½" × 5½" | 5¼" × 5¼" | Non-machinable surcharge |
| 6" Square | 6" × 6" | 5¾" × 5¾" | Non-machinable surcharge |
| 6½" Square | 6½" × 6½" | 6¼" × 6¼" | Non-machinable surcharge |
| 7" Square | 7" × 7" | 6¾" × 6¾" | Non-machinable surcharge |
| 8" Square | 8" × 8" | 7¾" × 7¾" | Non-machinable surcharge |
Square Envelope Important Notes:
- Additional postage required: USPS charges non-machinable surcharge (typically $0.20-0.30 extra)
- Hand-cancel recommended: To prevent damage during automated processing
- Popular for weddings: 6½" and 7" squares are common for invitations
- Premium appearance: Creates elegant, upscale impression
International Envelopes (C-Series / ISO 269)
Standard envelope sizes in most countries outside the US, designed to fit A-series paper sizes (A4, A5, etc.).
| Name | Size (mm) | Size (inches) | Fits Paper Size | Common Use |
|---|---|---|---|---|
| C6 | 114 × 162 mm | 4.5" × 6.4" | A6 (postcard) or A4 folded 4× | Postcards, small notes |
| C5 | 162 × 229 mm | 6.4" × 9" | A5 or A4 folded once | A4 letters folded |
| C4 | 229 × 324 mm | 9" × 12.8" | A4 unfolded | Full A4 documents |
| DL (DIN Lang) | 110 × 220 mm | 4.3" × 8.7" | A4 folded in thirds | Standard business (Europe) |
| C7 | 81 × 114 mm | 3.2" × 4.5" | A7 or A4 folded 5× | Small cards, gift enclosures |
| C3 | 324 × 458 mm | 12.8" × 18" | A3 unfolded | Posters, large documents |
C-Series Envelope System:
- Designed for A-series paper: Each C-size fits corresponding A-size
- DL most common: Standard business envelope in Europe (like #10 in US)
- Folding standards: C5 = A4 folded once; DL = A4 folded in thirds
- International mail: Use when sending to Europe, Asia, Australia
Specialty & Custom Envelopes
CD/DVD Envelopes
- Standard CD: 5" × 5" (fits standard CD jewel case)
- DVD Case: 5⅜" × 7½" (fits standard DVD case)
- CD/DVD Sleeves: 4⅞" × 5" (disc only, no case)
Photo Envelopes
| Photo Size | Envelope Size | Common Use |
|---|---|---|
| 3" × 5" | 3⅛" × 5⅛" | Small prints |
| 4" × 6" | 4⅛" × 6⅛" | Standard photo prints |
| 5" × 7" | 5⅛" × 7⅛" | Portrait photos |
| 8" × 10" | 8⅛" × 10⅛" | Large prints, certificates |
Specialty Sizes:
- Banker's flap: Traditional pointed flap for formal correspondence
- Policy envelope: 4" × 9" or 4½" × 10" for insurance documents
- Remittance: Dual-purpose with payment stub and return envelope
- Clasp/Metal clasp: Reusable envelopes with metal closure
- Expansion envelopes: Gusseted sides for thick documents
- String & button: Reusable with string-tie closure
Postage & Mailing Guidelines (USPS)
Standard Letter Mail Requirements:
- Minimum size: 3½" × 5" × 0.007" thick
- Maximum size: 6⅛" × 11½" × ¼" thick
- Weight: Up to 3.5 oz qualifies for letter rate
- Aspect ratio: Length ÷ height must be 1.3 to 2.5 (or non-machinable surcharge applies)
Large/Flat Mail Requirements:
- Size range: Exceeds letter size but not more than 12" × 15" × ¾" thick
- Weight: Up to 13 oz
- Cost: Higher postage than letters
Non-Machinable Surcharges Apply To:
- Square envelopes (any size)
- Envelopes with aspect ratio outside 1.3-2.5 range
- Envelopes with clasps, strings, or buttons
- Envelopes with rigid or irregular thickness
- Polyethylene or plastic envelopes
- Self-mailers with address on vertical edge
Save Money on Postage:
- Use standard sizes: #10 and A-series avoid surcharges
- Avoid square envelopes: Unless premium look is worth extra cost
- Stay under 1 oz: Letter rate increases at each ounce
- Pre-sort: Bulk mail rates available for large mailings
- Online postage: Often discounted vs. retail counter
Envelope Selection Guide
Choose #10 Business Envelope For:
- Standard 8.5" × 11" letters folded in thirds
- Professional business correspondence
- Invoices, statements, bills
- Most economical mailing option
Choose A-7 Announcement Envelope For:
- 5" × 7" invitations or cards
- Wedding invitations (most popular size)
- Formal announcements
- Greeting cards
Choose 9" × 12" Catalog Envelope For:
- 8.5" × 11" documents mailed flat (no folds)
- Contracts, legal documents, certificates
- Photos, artwork that shouldn't be creased
- Brochures, newsletters
Choose Square Envelope For:
- Premium, distinctive appearance
- Wedding invitations (when budget allows extra postage)
- Special announcements
- Square greeting cards
Choose C5/DL Envelope For:
- International correspondence
- A4 documents (standard outside US)
- Mailing to Europe, Asia, Australia
- Matching international paper standards