Envelope Size Reference
Enter an item size to find envelopes it fits, identify the closest standard envelope from measured dimensions, or browse 42 US and ISO sizes in inches, cm or mm with the USPS mail class of each.
The most common envelope sizes are the US #10 (4.125 x 9.5 in, 104.8 x 241.3 mm) for a letter folded in thirds, A7 (5.25 x 7.25 in) for 5 x 7 cards, 9 x 12 in (#10½ catalog) for flat letter paper, DL (110 x 220 mm) for A4 folded in thirds, and C4 (229 x 324 mm) for flat A4.
Use the Envelope Size Reference
Envelope size and fit calculator
Find the smallest standard envelope that fits an insert, or identify the closest standard format from physical measurements.
Dimensions shown are nominal exterior specifications. Standard manufacturing tolerances (typically ±1/16 in / 1.6 mm) and content thickness reduce usable interior room.
| Name | Width | Height | Fits | USPS class | Copy |
|---|---|---|---|---|---|
| #6¼ | 3.5 in | 6 in | Folded notes, small remittance slips | Letter | |
| #6¾ | 3.625 in | 6.5 in | Letter folded in quarters, checks | Letter | |
| #7 | 3.75 in | 6.75 in | Letter folded in quarters, personal checks | Letter | |
| #7¾ (Monarch) | 3.875 in | 7.5 in | Monarch sheet (7.25 × 10.5 in) folded in thirds | Letter | |
| #8⅝ | 3.625 in | 8.625 in | Checks and statements; nests inside a #10 | Letter | |
| #9 | 3.875 in | 8.875 in | Letter folded in thirds; fits inside a #10 | Letter | |
| #10 | 4.125 in | 9.5 in | US Letter (8.5 × 11 in) folded in thirds | Letter | |
| #11 | 4.5 in | 10.375 in | Letter folded in thirds with room for inserts | Letter | |
| #12 | 4.75 in | 11 in | Legal (8.5 × 14 in) folded in thirds | Letter | |
| #14 | 5 in | 11.5 in | Legal folded, thick inserts | Letter | |
| A1 | 3.625 in | 5.125 in | 3.5 × 4.875 in card | Letter | |
| A2 | 4.375 in | 5.75 in | 4.25 × 5.5 in card (letter sheet folded in quarters) | Letter | |
| A4 | 4.25 in | 6.25 in | 4 × 6 in photo or card (snug) | Letter | |
| A6 | 4.75 in | 6.5 in | 4.5 × 6.25 in card or 4 × 6 photo | Letter | |
| A7 | 5.25 in | 7.25 in | 5 × 7 in card or photo | Letter | |
| A8 | 5.5 in | 8.125 in | 5.25 × 7.875 in card | Letter | |
| A9 | 5.75 in | 8.75 in | 5.5 × 8.5 in card (half letter) | Letter | |
| A10 | 6 in | 9.5 in | 5.75 × 9.25 in card | Letter | |
| 5½ square | 5.5 in | 5.5 in | 5.25 × 5.25 in card | Letter, nonmachinable | |
| 6 square | 6 in | 6 in | 5.75 × 5.75 in card | Letter, nonmachinable | |
| 6½ square | 6.5 in | 6.5 in | 6.25 × 6.25 in card | Flat (large envelope) | |
| #1 catalog (6×9) | 6 in | 9 in | Letter folded once, booklets, 5.5 × 8.5 in flat | Letter | |
| #1¾ catalog | 6.5 in | 9.5 in | 6 × 9 in booklet | Flat (large envelope) | |
| #3 catalog | 7 in | 10 in | 6.5 × 9.5 in booklet | Flat (large envelope) | |
| #6 catalog | 7.5 in | 10.5 in | 7 × 10 in booklet | Flat (large envelope) | |
| #9¾ catalog | 8.75 in | 11.25 in | 8.5 × 11 in sheets (snug) | Flat (large envelope) | |
| #10½ catalog (9×12) | 9 in | 12 in | Unfolded 8.5 × 11 in US Letter | Flat (large envelope) | |
| #12½ catalog | 9.5 in | 12.5 in | Letter-size folders, thicker packets | Flat (large envelope) | |
| #13½ catalog (10×13) | 10 in | 13 in | Unfolded letter with thick margin or binding | Flat (large envelope) | |
| #14½ catalog | 11.5 in | 14.5 in | Legal size flat, oversized catalogs | Flat (large envelope) | |
| #15½ catalog | 12 in | 15.5 in | 11 × 14 in prints, tabloid folded once | Parcel | |
| C7 | 3.189 in | 4.488 in | A7 (74 × 105 mm) flat | Too small for USPS | |
| C6 | 4.488 in | 6.378 in | A6 flat, A4 folded twice, A5 folded once | Letter | |
| DL | 4.331 in | 8.661 in | A4 folded in thirds (99 × 210 mm insert) | Letter | |
| C6/C5 (C65) | 4.488 in | 9.016 in | A4 folded in thirds with more room, DL insert | Letter | |
| C5 | 6.378 in | 9.016 in | A5 flat, A4 folded once | Flat (large envelope) | |
| C4 | 9.016 in | 12.756 in | A4 flat (210 × 297 mm), B5 folded once | Flat (large envelope) | |
| C3 | 12.756 in | 18.031 in | A3 flat (297 × 420 mm), B4 folded | Parcel | |
| B6 | 4.921 in | 6.929 in | C6 envelope or A6 card with margin | Letter | |
| B5 | 6.929 in | 9.843 in | C5 envelope, A5 booklet with margin | Flat (large envelope) | |
| B4 | 9.843 in | 13.898 in | C4 envelope, thick A4 packets | Flat (large envelope) | |
| E4 | 11.024 in | 15.748 in | B4 envelope, bulky A4 files | Parcel |
USPS class is derived from the nominal size alone and assumes the address runs along the long side, thickness within the class limit (0.25 in for letters, 0.75 in for flats) and a flexible paper envelope. Letters weigh up to 3.5 oz.
Dimensional Standards and Unit Relationships
USPS dimensional standards (DMM 101)
- Letter: 5 to 11.5 in long, 3.5 to 6.125 in high, 0.007 to 0.25 in thick, up to 3.5 oz.
- Nonmachinable letter: length ÷ height below 1.3 or above 2.5 (square letter-size envelopes), rigid, clasps or strings, lumpy contents, or address parallel to the short side. A surcharge applies.
- Flat (large envelope): over any letter maximum, up to 15 × 12 × 0.75 in, flexible and uniformly thick. Larger pieces mail as parcels.
- USPS DMM 101: Physical Standards
Manufacturing tolerances & units
- Units: 1 inch = exactly 25.4 mm. ISO 269 / DIN 678 envelopes (C, DL, B, E) are defined in whole millimetres; US sizes are defined in inches.
- C-series rule: a C envelope fits the A sheet of the same number flat (C4 takes A4, C5 takes A5); a B envelope fits the C envelope of the same number.
- Tolerance: normal manufacturing tolerance is about ±1/16 in (1.6 mm). Allow at least 1/8 in (3 mm) per side for a single card, more for booklets or multi-page inserts.
Quick answer
The most common envelope sizes are the US #10 (4.125 x 9.5 in, 104.8 x 241.3 mm) for a letter folded in thirds, A7 (5.25 x 7.25 in) for 5 x 7 cards, 9 x 12 in (#10½ catalog) for flat letter paper, DL (110 x 220 mm) for A4 folded in thirds, and C4 (229 x 324 mm) for flat A4.
Example: a 24 cm x 11 cm envelope is closest to a US #10 (24.1 x 10.5 cm), only about 5.4 mm off; a DL (22 x 11 cm) is 2 cm shorter
Enter your item or envelope size to find a fitting or matching standard envelope.
Summary
This reference covers 42 standard envelope formats used in the US, Europe and internationally: US commercial (#6¼ to #14), announcement (A1 to A10), square, catalog (#1 to #15½), ISO C-series and DL, and B and E sizes. Each entry lists nominal dimensions in inches, centimeters and millimeters, typical contents, and the USPS dimensional class computed from the size: machinable letter, nonmachinable letter (aspect ratio outside 1.3 to 2.5), flat or parcel. Filter by group, search by keyword, or calculate fits with custom clearance.
How it works
- Choose whether to find a suitable envelope for an insert or identify an existing envelope from measured dimensions.
- Enter width, height and unit (cm, mm or inches), plus optional clearance per side; the result also shows the USPS class of your size.
- Filter the chart by group (US Commercial, Announcement, Square, Catalog, ISO C-Series or B/E series) or search by name or use.
- Toggle the table between inches, centimeters and millimeters.
- Click the Copy button on any row to copy formatted dimensions to your clipboard.
Use cases
- Choose the right envelope for folded letters, invoices, greeting cards or photos.
- Find catalog sizes (6×9 to 12×15½ in) for unfolded documents and marketing packets.
- Check whether an envelope mails as a USPS letter, a nonmachinable letter, a flat or a parcel before printing.
- Select ISO C-series envelopes for A-series documents (C4 for unfolded A4, C5 for A5 or half-fold A4, DL for tri-fold A4).
- Identify an unlabelled envelope from a ruler measurement.
- Convert envelope dimensions between inches, centimeters and millimeters for prepress and packaging setup.