Envelope Sizes Chart: US and International Dimensions
US envelopes are named by number and letter (#10, A7, 9 × 12 catalog) and international envelopes by ISO code (DL, C5, C4). These charts give each size in inches and millimeters, what it is made to hold, and how postal rules treat it.
The standard US business envelope is the #10, 4 1/8 × 9 1/2 in (105 × 241 mm), which holds a Letter sheet folded in thirds. The common invitation envelope is the A7, 5 1/4 × 7 1/4 in (133 × 184 mm) for 5 × 7 cards. Internationally, the DL (110 × 220 mm) takes A4 folded in thirds, C5 (162 × 229 mm) takes A4 folded once and C4 (229 × 324 mm) takes A4 flat.
- #10 business
- 4 1/8 × 9 1/2 in
- A7 invitation
- 5 1/4 × 7 1/4 in
- DL
- 110 × 220 mm
- Catalog for Letter
- 9 × 12 in
On this page
Envelope size chart: the sizes used most
Envelopes are listed short side first (height × length). Sizes are the outside dimensions; the space for the contents is about 1/8 to 1/4 in (3 to 6 mm) smaller in each direction.
| Envelope | Inches | mm | Made for |
|---|---|---|---|
| #10 business | 4 1/8 × 9 1/2 | 105 × 241 | Letter folded in thirds |
| #9 reply | 3 7/8 × 8 7/8 | 98 × 225 | Return envelope inside a #10 |
| #6 3/4 personal | 3 5/8 × 6 1/2 | 92 × 165 | Bill payments, checks, small notes |
| A2 | 4 3/8 × 5 3/4 | 111 × 146 | 4 1/4 × 5 1/2 in cards, RSVPs |
| A7 | 5 1/4 × 7 1/4 | 133 × 184 | 5 × 7 in cards and invitations |
| 6 × 9 catalog/booklet | 6 × 9 | 152 × 229 | Letter folded once, booklets |
| 9 × 12 catalog | 9 × 12 | 229 × 305 | Letter or A4 flat |
| 10 × 13 catalog | 10 × 13 | 254 × 330 | Letter in a folder, thick documents |
| DL | 4.33 × 8.66 | 110 × 220 | A4 folded in thirds |
| C5 | 6.38 × 9.02 | 162 × 229 | A4 folded once, A5 flat |
| C4 | 9.02 × 12.76 | 229 × 324 | A4 flat |
Business envelope sizes (commercial and official)
Commercial envelopes are long and narrow with the flap on the long side. They carry folded letters, invoices and statements. The #10 is the default for business mail in the US; the others cover smaller paper and thicker contents.
| Size | Inches | mm | Typical contents |
|---|---|---|---|
| #6 1/4 | 3 1/2 × 6 | 89 × 152 | Small notes, remittance slips |
| #6 3/4 | 3 5/8 × 6 1/2 | 92 × 165 | Personal checks, bill payments |
| #7 | 3 3/4 × 6 3/4 | 95 × 171 | Personal letters |
| #7 3/4 (Monarch) | 3 7/8 × 7 1/2 | 98 × 190 | Monarch stationery (7 1/4 × 10 1/2 in) folded in thirds |
| #8 5/8 (check) | 3 5/8 × 8 5/8 | 92 × 219 | Business checks, payroll |
| #9 | 3 7/8 × 8 7/8 | 98 × 225 | Reply envelope, Letter in thirds |
| #10 | 4 1/8 × 9 1/2 | 105 × 241 | Letter in thirds, up to about 5 sheets |
| #11 | 4 1/2 × 10 3/8 | 114 × 264 | Thicker Letter mailings |
| #12 | 4 3/4 × 11 | 121 × 279 | Legal folded in thirds (snug), bulky documents |
| #14 | 5 × 11 1/2 | 127 × 292 | Legal folded in thirds, policies, contracts |
Window envelopes come in the same sizes. The most common #10 window is 1 1/8 × 4 1/2 in, set 7/8 in from the left and 1/2 in from the bottom, but positions vary by manufacturer, so print a test sheet before a large run. Address placement for each paper size is covered in the envelopes for paper sizes guide.
Invitation and greeting card envelopes (A-style)
A-style or announcement envelopes are squarer than business envelopes and usually have a deep square or pointed flap. Each holds a card about 1/8 in narrower and 1/4 in shorter than the envelope. These A numbers have nothing to do with A4 or A5 paper.
| Size | Envelope (in) | Envelope (mm) | Card size (in) |
|---|---|---|---|
| A1 (4 Bar) | 3 5/8 × 5 1/8 | 92 × 130 | 3 1/2 × 4 7/8 (RSVP, place cards) |
| A2 | 4 3/8 × 5 3/4 | 111 × 146 | 4 1/4 × 5 1/2 (Letter quartered) |
| A6 | 4 3/4 × 6 1/2 | 121 × 165 | 4 1/2 × 6 1/4, or 4 × 6 photos |
| A7 | 5 1/4 × 7 1/4 | 133 × 184 | 5 × 7 (invitations, greeting cards) |
| A8 | 5 1/2 × 8 1/8 | 140 × 206 | 5 1/4 × 7 7/8 |
| A9 | 5 3/4 × 8 3/4 | 146 × 222 | 5 1/2 × 8 1/2 (Letter folded in half) |
| A10 | 6 × 9 1/2 | 152 × 241 | Tall cards and programs, up to about 5 3/4 × 9 1/4 |
The 1/4 in allowance is for a single card. A 5 × 7 card with a backing layer, ribbon or RSVP set inside often jams in an A7; use an A8 or a Euro flap envelope sized for the full stack, and weigh the finished piece before buying postage.
Square envelope sizes
Square envelopes are common at 5 × 5, 5 1/2 × 5 1/2, 6 × 6, 6 1/2 × 6 1/2 and 7 1/2 × 7 1/2 in (127, 140, 152, 165 and 190 mm). In the US they always pay the nonmachinable surcharge, explained below.
Catalog and booklet envelopes
Large envelopes come in two styles in the same sizes. Catalog envelopes open on the short end, which suits stacks pushed in lengthwise. Booklet envelopes open on the long side, which suits inserting machines and bound booklets.
| Size | Inches | mm | Holds |
|---|---|---|---|
| #1 | 6 × 9 | 152 × 229 | Letter folded once, Half Letter booklets |
| #1 3/4 | 6 1/2 × 9 1/2 | 165 × 241 | Thicker folded mailings |
| #3 | 7 × 10 | 178 × 254 | Small catalogs, Half Letter booklets with bulk |
| #6 | 7 1/2 × 10 1/2 | 190 × 267 | B5 booklets and notebooks |
| #9 3/4 | 8 3/4 × 11 1/4 | 222 × 286 | Letter flat, very snug |
| #10 1/2 | 9 × 12 | 229 × 305 | Letter or A4 flat |
| #12 1/2 | 9 1/2 × 12 1/2 | 241 × 318 | Letter with a few dozen sheets |
| #13 1/2 | 10 × 13 | 254 × 330 | Letter in a pocket folder |
| #14 1/2 | 11 1/2 × 14 1/2 | 292 × 368 | Legal flat, binders |
| #15 1/2 | 12 × 15 1/2 | 305 × 394 | Tabloid folded, large catalogs |
Padded mailers and bubble mailers use their own numbering (#0, #2, #5 and so on) and vary by maker. For anything thicker than 3/4 in, compare shipping box sizes instead, since it will be priced as a parcel either way.
International envelope sizes (ISO C, B and DL)
ISO 269 sizes envelopes to the A paper series. A C envelope holds the A sheet of the same number flat, and B envelopes are larger again for thick contents.
| Size | mm | Inches | Holds |
|---|---|---|---|
| C3 | 324 × 458 | 12.8 × 18.0 | A3 flat, A4 files |
| B4 | 250 × 353 | 9.8 × 13.9 | A4 with bulk, catalogs |
| C4 | 229 × 324 | 9.0 × 12.8 | A4 flat |
| B5 | 176 × 250 | 6.9 × 9.8 | A5 booklets, C5 contents with bulk |
| C5 | 162 × 229 | 6.4 × 9.0 | A5 flat, A4 folded once |
| C6/C5 | 114 × 229 | 4.5 × 9.0 | A4 folded in thirds, roomier than DL |
| DL | 110 × 220 | 4.3 × 8.7 | A4 folded in thirds |
| C6 | 114 × 162 | 4.5 × 6.4 | A6 cards, A4 folded twice |
| C7 | 81 × 114 | 3.2 × 4.5 | A7 cards, gift tags |
The DL is not part of the C series; its name comes from the German "DIN Lang". It is the European counterpart to the #10 and is about 5 mm wider and 21 mm shorter.
Postal size limits for envelopes
Postage depends on size and shape as much as weight. These limits were current in 2026; check with the postal service before a large mailing.
United States (USPS)
| Category | Height | Length | Thickness |
|---|---|---|---|
| Postcard rate | 3 1/2 to 4 1/4 in | 5 to 6 in | 0.007 to 0.016 in |
| Letter | 3 1/2 to 6 1/8 in | 5 to 11 1/2 in | 0.007 to 1/4 in |
| Flat (large envelope) | Up to 12 in | Up to 15 in | Up to 3/4 in |
- Aspect ratio: a letter's length divided by its height must be between 1.3 and 2.5, or it pays the nonmachinable surcharge. A #10 is 2.30, an A7 1.38 and an A2 1.31, just inside the limit. Every square envelope fails.
- Other nonmachinable triggers: clasps, strings or buttons, rigid contents or uneven thickness. Separately, a letter heavier than 3.5 oz is priced as a flat.
- Size jumps: a 6 × 9 envelope still qualifies as a letter, but a 6 1/2 × 9 1/2 does not and pays the higher flat price. A 12 × 15 1/2 envelope exceeds the flat limit and is priced as a parcel.
United Kingdom (Royal Mail)
- Letter: up to 240 × 165 × 5 mm and 100 g. C5, C6 and DL envelopes qualify.
- Large Letter: up to 353 × 250 × 25 mm and 750 g. C4 and B4 envelopes qualify; anything thicker than 25 mm is a parcel.
How to measure an envelope
- Close the flap and measure the finished rectangle. Flap depth is never included in the listed size.
- Measure the short side first. Envelope sizes are quoted height × length, so a #10 is written 4 1/8 × 9 1/2.
- Check the opening. If it opens on the short end it is a catalog envelope; on the long side, a booklet, commercial or announcement envelope.
- Size the contents with clearance. Allow at least 1/4 in (6 mm) on length and width for flat contents, plus the contents' thickness on each dimension for anything bulkier than a few sheets.
For the paper behind these sizes, see the paper sizes chart and the A4 paper guide. If you are mailing prints, the photo print sizes page lists which envelope suits 4 × 6, 5 × 7 and 8 × 10 photos.
Frequently asked questions
What size envelope do I need for 8.5 × 11 paper unfolded?
A 9 × 12 in catalog or booklet envelope (229 × 305 mm). It leaves 1/4 in at each side and 1/2 in at the end. For thick stacks or a folder, step up to 10 × 13 in.
What size is a standard greeting card envelope?
Most greeting cards are 5 × 7 in and go in an A7 envelope (5 1/4 × 7 1/4 in). Smaller 4 1/4 × 5 1/2 in thank-you cards use the A2 (4 3/8 × 5 3/4 in), and 4 × 6 in cards or photos use the A6 (4 3/4 × 6 1/2 in).
What is the difference between a #9 and a #10 envelope?
A #9 is 3 7/8 × 8 7/8 in, 1/4 in shorter and 5/8 in narrower than a #10 (4 1/8 × 9 1/2 in). Both hold a Letter sheet folded in thirds, and the #9 is used as a reply envelope because it fits inside a #10 without folding.
Does a square envelope cost more to mail?
In the US, yes. A square envelope fails the USPS aspect-ratio rule (length divided by height must be 1.3 to 2.5), so it is nonmachinable and pays a surcharge on top of the First-Class letter price.
What does the number on an envelope mean?
Nothing you can calculate. US commercial numbers (#6 3/4, #10, #14) and catalog numbers (#1, #10 1/2, #13 1/2) are trade designations that grew larger with the envelope. A-style sizes (A2, A7) are a separate series for cards and are unrelated to ISO A paper.
What size is a 6 × 9 envelope in mm?
152 × 229 mm. It holds a Letter sheet folded in half or a Half Letter booklet, and at under 1/4 in thick it still mails as a letter in the US because its height (6 in) is within the 6 1/8 in limit.