Envelope Sizes Guide
Standard US #10 business envelopes are 9.5 × 4.125 in (241 × 105 mm). A4 letters fit a C4 envelope (324 × 229 mm); folded in thirds they fit DL (220 × 110 mm). Full chart and finder below.
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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 |
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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