Envelope Sizes: Complete US & International Guide
The #10 envelope (4.125 x 9.5 inches) is the standard US business envelope, fitting a letter-size sheet folded into thirds. In international markets, the DL envelope (110 x 220 mm) serves the same purpose for A4 paper. This guide covers every standard envelope size across US commercial, US A-series (announcement), and ISO C-series formats with exact dimensions in both inches and millimeters.
US Commercial Envelopes
Commercial envelopes are the standard for business correspondence in the United States. They are numbered from #6 1/4 through #14, with larger numbers indicating larger envelopes. All dimensions below are width x height (the width is the longer dimension for commercial envelopes).
| Envelope | Inches (W x H) | Millimeters (W x H) | Common Use |
|---|---|---|---|
| #6 1/4 | 6 x 3.5 | 152.4 x 88.9 | Remittance, reply envelopes |
| #6 3/4 | 6.5 x 3.625 | 165.1 x 92.1 | Personal letters, remittance |
| #7 | 6.75 x 3.75 | 171.5 x 95.3 | Personal correspondence |
| #7 3/4 (Monarch) | 7.5 x 3.875 | 190.5 x 98.4 | Executive/monarch letterhead |
| #9 | 8.875 x 3.875 | 225.4 x 98.4 | Return envelopes (fits inside #10) |
| #10 | 9.5 x 4.125 | 241.3 x 104.8 | Standard business envelope |
| #11 | 10.375 x 4.5 | 263.5 x 114.3 | Statements, invoices |
| #12 | 11 x 4.75 | 279.4 x 120.7 | Catalogs, larger documents |
| #14 | 11.5 x 5 | 292.1 x 127 | Legal documents, oversize mail |
Key Commercial Envelope Notes
- The #10 envelope is by far the most widely used. Nearly all pre-printed business envelopes, bank statements, and official correspondence use this size.
- The #9 envelope is designed as a return envelope that fits inside a #10. Many businesses include a #9 reply envelope in their #10 mailings.
- The #7 3/4 (Monarch) fits monarch-size stationery (7.25 x 10.5 inches), commonly used for executive correspondence.
US A-Series (Announcement) Envelopes
A-series envelopes are designed for cards, invitations, announcements, and photos. They have wider proportions than commercial envelopes, making them suitable for greeting cards and RSVP enclosures. Dimensions listed are width x height.
| Envelope | Inches (W x H) | Millimeters (W x H) | Fits Card Size | Common Use |
|---|---|---|---|---|
| A1 (3 Bar) | 5.125 x 3.625 | 130.2 x 92.1 | 3.5 x 5 in | RSVP cards, gift enclosures |
| A2 (5.5 Bar) | 5.75 x 4.375 | 146.1 x 111.1 | 4.25 x 5.5 in | Note cards, RSVP cards |
| A6 (6 Bar) | 6.5 x 4.75 | 165.1 x 120.7 | 4.5 x 6.25 in | Invitations, photo prints (4x6) |
| A7 (7 Bar) | 7.25 x 5.25 | 184.2 x 133.4 | 5 x 7 in | 5x7 invitations, greeting cards |
| A8 | 8.125 x 5.5 | 206.4 x 139.7 | 5.25 x 7.875 in | Large invitations, programs |
| A9 | 8.75 x 5.75 | 222.3 x 146.1 | 5.5 x 8.5 in | Large cards, half-fold letters |
| A10 | 9.5 x 6 | 241.3 x 152.4 | 6 x 9.25 in | Booklets, catalogs |
Selecting the Right A-Series Envelope
Choose an envelope that provides at least 0.125 inches (3 mm) clearance on each side beyond your card or insert. This ensures the card slides in and out without binding. For example, a 5 x 7 inch invitation fits perfectly in an A7 (7.25 x 5.25 inches) with approximately 0.125 inches of clearance on each dimension.
ISO C-Series Envelopes (International)
The ISO 269 standard defines C-series envelopes specifically to fit ISO A-series paper. Each C-size envelope is designed to hold the corresponding A-size sheet. The DL format, while not officially part of the numbered C-series, is included because it is the most common international business envelope.
| Envelope | Millimeters (W x H) | Inches (W x H) | Fits Paper Size | Common Use |
|---|---|---|---|---|
| C3 | 324 x 458 | 12.76 x 18.03 | A3 unfolded | Large documents, posters |
| C4 | 229 x 324 | 9.02 x 12.76 | A4 unfolded | Reports, manuscripts |
| C5 | 162 x 229 | 6.38 x 9.02 | A4 folded once, A5 unfolded | Half-fold letters, A5 cards |
| C6 | 114 x 162 | 4.49 x 6.38 | A4 folded twice, A5 folded once, A6 unfolded | Personal letters, invitations |
| C7 | 81 x 114 | 3.19 x 4.49 | A7 unfolded | Small cards, coin envelopes |
| DL | 110 x 220 | 4.33 x 8.66 | A4 folded into thirds, A5 folded once | Standard European business envelope |
How ISO C-Series Envelopes Relate to A-Series Paper
The C-series dimensions are the geometric mean between the corresponding A-series and B-series sizes. In practical terms:
- C4 holds A4 flat — no folding required.
- C5 holds A4 folded in half or A5 flat.
- C6 holds A4 folded into quarters, A5 folded in half, or A6 flat.
- DL holds A4 folded into thirds — the most common configuration for business letters in Europe, Australia, and much of Asia.
For full A-series paper dimensions, see our A-Series Paper Sizes guide.
Paper Size to Envelope Compatibility
This cross-reference table shows which envelopes work with common paper and card sizes.
| Paper / Card Size | Fold Method | Recommended US Envelope | Recommended ISO Envelope |
|---|---|---|---|
| US Letter (8.5 x 11 in) | Tri-fold | #10 (4.125 x 9.5 in) | — |
| US Letter (8.5 x 11 in) | Half-fold | 6 x 9 catalog | — |
| US Legal (8.5 x 14 in) | Tri-fold | #10 (4.125 x 9.5 in) | — |
| A4 (210 x 297 mm) | No fold | — | C4 (229 x 324 mm) |
| A4 (210 x 297 mm) | Half-fold | — | C5 (162 x 229 mm) |
| A4 (210 x 297 mm) | Tri-fold | — | DL (110 x 220 mm) |
| A5 (148 x 210 mm) | No fold | — | C5 (162 x 229 mm) |
| 5 x 7 in card | No fold | A7 (5.25 x 7.25 in) | — |
| 4 x 6 in card/photo | No fold | A6 (4.75 x 6.5 in) | — |
| 4.25 x 5.5 in card | No fold | A2 (4.375 x 5.75 in) | — |
| Business card (3.5 x 2 in) | No fold | #6 1/4 or coin envelope | — |
For US paper dimensions, see our US Paper Sizes guide.
Catalog and Booklet Envelopes
Beyond commercial and announcement sizes, two other US envelope categories serve specialized needs:
Catalog Envelopes
Catalog envelopes open on the short side and are used for thick documents, booklets, and magazines.
| Size Name | Inches (W x H) | Millimeters (W x H) |
|---|---|---|
| 6 x 9 | 6 x 9 | 152.4 x 228.6 |
| 7 x 10 | 7 x 10 | 177.8 x 254 |
| 9 x 12 | 9 x 12 | 228.6 x 304.8 |
| 9.5 x 12.5 | 9.5 x 12.5 | 241.3 x 317.5 |
| 10 x 13 | 10 x 13 | 254 x 330.2 |
Booklet Envelopes
Booklet envelopes open on the long side, making them easier to stuff with large, flat items like brochures and booklets.
| Size Name | Inches (W x H) | Millimeters (W x H) |
|---|---|---|
| 6 x 9 | 6 x 9 | 152.4 x 228.6 |
| 6.5 x 9.5 | 6.5 x 9.5 | 165.1 x 241.3 |
| 9 x 12 | 9 x 12 | 228.6 x 304.8 |
| 10 x 13 | 10 x 13 | 254 x 330.2 |
USPS Mailing Requirements
For US mailings, the United States Postal Service (USPS) sets size requirements that affect postage rates:
Letter-Size Mail
- Minimum: 3.5 x 5 inches (88.9 x 127 mm)
- Maximum: 6.125 x 11.5 inches (155.6 x 292.1 mm)
- Maximum thickness: 0.25 inches (6.35 mm)
- Aspect ratio: between 1.3 and 2.5 (length divided by height)
Envelopes that fall outside these dimensions are classified as flats or parcels and incur higher postage.
Non-Machinable Surcharge
A surcharge applies to letter-size mail that is:
- Square (aspect ratio of 1:1)
- Too rigid or too thick (over 0.25 inches)
- Has clasps, strings, or buttons
- Contains items that cause uneven thickness
The #10 and DL envelopes both meet standard letter-size mailing requirements without surcharges.
Envelope Materials and Weights
| Material | Weight Range | Best For |
|---|---|---|
| Wove (smooth) | 70-90 gsm | Standard business correspondence |
| Laid (textured) | 80-120 gsm | Premium stationery, formal invitations |
| Kraft (brown) | 70-120 gsm | Shipping, eco-friendly mailings |
| Tyvek | N/A (synthetic) | Tear-resistant, moisture-resistant mailings |
| Cotton/rag | 90-120 gsm | Luxury invitations, legal documents |
Window Envelope Specifications
Window envelopes have a transparent panel that displays the recipient’s address printed directly on the enclosed document, eliminating the need to print on the envelope itself.
Standard Window Position (#10 Envelope)
- Window size: 1.125 x 4.5 inches (28.6 x 114.3 mm)
- From left edge: 0.875 inches (22.2 mm)
- From bottom edge: 0.5 inches (12.7 mm)
When designing letters for window envelopes, position the address block to align with the window when the letter is tri-folded. The address should have at least 0.125 inches (3 mm) of clearance from all window edges to remain visible even with slight folding variations.
Printing on Envelopes
Resolution and Setup
- Resolution: 300 DPI for sharp text and logos.
- Color mode: CMYK for full-color printing; grayscale or black-only for most business envelopes.
- Bleed: Not standard for envelopes. Most envelope printing does not extend to the edge. If full-bleed printing is required, confirm capability with your printer.
- Safe area: Keep text at least 0.25 inches (6.35 mm) from all edges.
Return Address Placement
- US standard: Upper left corner, at least 0.25 inches from the top and left edges.
- Postage area: Upper right corner, reserved for stamps or meter marks.
Related Resources
- A-Series Paper Sizes — A0 through A10 dimensions and specifications
- US Paper Sizes — letter, legal, tabloid, and ANSI standards
- Business Card Sizes — standard dimensions by country
Frequently Asked Questions
What size is a #10 envelope?
A #10 envelope measures 4.125 x 9.5 inches (104.8 x 241.3 mm). It is the standard US business envelope and fits a letter-size sheet folded into thirds.
What envelope fits an A4 sheet without folding?
A C4 envelope (229 x 324 mm / 9.02 x 12.76 inches) fits an A4 sheet without folding. A C5 envelope (162 x 229 mm) fits A4 folded in half, and a DL envelope (110 x 220 mm) fits A4 folded into thirds.
What is a DL envelope?
A DL (Dimension Lengthwise) envelope measures 110 x 220 mm (4.33 x 8.66 inches). It is the most common business envelope in Europe and fits an A4 sheet folded into thirds or an A5 sheet folded in half.
What envelope size do I need for a 5x7 card?
Use an A7 envelope, which measures 5.25 x 7.25 inches (133.4 x 184.2 mm). This provides approximately 0.125 inches of clearance on each side for a standard 5 x 7 inch card or invitation.
What is the difference between commercial and A-series envelopes?
US commercial envelopes (numbered #6 through #14) are designed for business correspondence and fit standard letter-size paper when folded. US A-series (announcement) envelopes are designed for cards, invitations, and photos, with wider proportions than commercial envelopes.