No. 10 envelope size in inches, mm and cm
No. 10 envelope is 104.8 × 241.3 mm (4.12 × 9.5 inches).
No. 10 envelope dimensions
| Unit | Width | Length |
|---|---|---|
| Millimetres | 104.8 mm | 241.3 mm |
| Centimetres | 10.48 cm | 24.13 cm |
| Inches | 4.12 in | 9.5 in |
| Points (1/72 in) | 297 | 684 |
Shape: length is 2.303 times the width.
The No. 10 is the standard business envelope in the United States. It is sold plain, windowed and with a self-seal flap, and is the usual size for invoices, statements and form letters.
What fits in a No. 10 envelope envelope
The first fold that leaves at least 3 mm to spare each way is shown. “Does not fit” means no fold up to quarters fits.
| Sheet | How it fits | Size when folded | Spare (width, length) |
|---|---|---|---|
| US Letter | folded in three (letter fold) | 216 × 93 mm | 12 × 25 mm |
| A4 | folded in three (letter fold) | 210 × 99 mm | 6 × 31 mm |
| US Legal | does not fit | - | - |
| Half Letter (Statement) | folded in three (letter fold) | 140 × 72 mm | 33 × 102 mm |
| A5 | folded in three (letter fold) | 148 × 70 mm | 35 × 93 mm |
| A6 | folded in half | 105 × 74 mm | 31 × 136 mm |
Spare is the envelope dimension minus the folded sheet, in mm. Real envelopes vary a little between makers, and a thick insert needs extra room.
US Letter folded in three
A US Letter sheet (8.5 × 11 in) folded in three, 3.67 in tall, slides into a No. 10 envelope (4.125 in tall) with 0.46 in to spare in height and 1.0 in in length. An A4 sheet folded in three is 210 × 99 mm; the No. 10 is 241.3 mm long and 104.8 mm tall, so it fits with 31 mm spare lengthwise but only 5.8 mm in height. That is tight for a window envelope, so check your merge layout.
No. 10 vs DL
The No. 10 (104.8 × 241.3 mm) is 5.2 mm shorter and 21.3 mm longer than DL (110 × 220 mm). An A4 letter folded for a DL envelope fits a No. 10, and a Letter folded in three fits a DL, but with only 4 mm to spare along the length.
USPS letter-size limits
The United States Postal Service defines a letter-size mailpiece in its Domestic Mail Manual, section 201: not less than 5 inches long, 3-1/2 inches high and 0.007 inch thick, and not more than 11-1/2 inches long, 6-1/8 inches high and 1/4 inch thick. A No. 10 is well inside those limits (9.5 × 4.125 in). Source: USPS DMM 201, section 1.1.1, checked 27 October 2026. Pieces outside the aspect ratio rules or thicker than the limits can cost more to mail; check the DMM or ask your post office.
Frequently asked questions
What size is a No. 10 envelope?
A No. 10 envelope is 4 1/8 x 9 1/2 inches (104.8 x 241.3 mm).
Does a Letter sheet fit a No. 10 envelope?
Yes, folded in thirds: the folded sheet is 8.5 x 3.67 inches.
Does A4 fit a No. 10 envelope?
Yes, folded in three (210 x 99 mm), but with only 5.8 mm to spare in height.
Is a No. 10 envelope the same as DL?
No. DL is 110 x 220 mm; No. 10 is 104.8 x 241.3 mm.
What are the USPS maximum letter dimensions?
USPS says letters can be no more than 11-1/2 inches long, 6-1/8 inches high and 1/4 inch thick (Domestic Mail Manual 201).