Envelope Sizes Chart: US and International

The exact size of every common envelope, what each one is made to hold, which envelope fits a letter or a greeting card, and the USPS size limits for a regular stamp.

Updated

Envelopes drawn to the same scale: A2, A7, #10, 6 × 9 and 9 × 12 inch, each labeled with its size and what it holds

Envelope sizes come in families, each made for something specific: number sizes (#10, #9) for folded letters, A sizes (A2, A7) for greeting cards and invitations, catalog sizes (6 × 9, 9 × 12) for flat documents, and the international ISO sizes (DL, C5, C4) made for A4 paper.

US envelope sizes

Envelope Inches mm Holds
#6¾ 3⅝ × 6½ 92 × 165 Personal letters, bills, checks
Monarch (#7¾) 3⅞ × 7½ 98 × 191 Personal stationery (7¼ × 10½ paper)
#9 3⅞ × 8⅞ 98 × 225 Return envelope inside a #10
#10 4⅛ × 9½ 105 × 241 US Letter folded in thirds: the standard business envelope
A2 4⅜ × 5¾ 111 × 146 4¼ × 5½ cards (a Letter sheet folded into quarters)
A6 4¾ × 6½ 121 × 165 4 × 6 photos and cards
A7 5¼ × 7¼ 133 × 184 5 × 7 cards and invitations
A9 5¾ × 8¾ 146 × 222 5½ × 8½ cards (a Letter sheet folded in half)
A10 6 × 9½ 152 × 241 6 × 9 cards
6 × 9 6 × 9 152 × 229 Booklets, Letter folded in half
9 × 12 9 × 12 229 × 305 US Letter or A4 unfolded
10 × 13 10 × 13 254 × 330 Letter unfolded with room for a folder or several pages

The rule for cards and photos: choose an envelope about ¼ inch larger than what goes inside, in both directions.

International (ISO) envelope sizes

Envelope mm Inches Holds
DL 110 × 220 4.33 × 8.66 A4 folded in thirds
C6 114 × 162 4.49 × 6.38 A4 folded in quarters, or A6 cards
C5 162 × 229 6.38 × 9.02 A4 folded in half, or A5 flat
C4 229 × 324 9.02 × 12.76 A4 flat

The C sizes are designed around the A paper sizes: C4 holds A4, C5 holds A5 and C6 holds A6, each with a few millimeters to spare.

Which envelope do I need?

You’re sending Use
A letter on US Letter paper, folded in thirds #10
A letter on A4 paper, folded in thirds DL
A 5 × 7 invitation A7
A 4 × 6 photo or card A6
A folded card from a Letter sheet (5½ × 8½) A9
Documents you don’t want folded 9 × 12 (Letter) or C4 (A4)

USPS size limits

For the regular letter price, an envelope must be:

  • At least 3½ × 5 inches and no more than 6⅛ × 11½ inches.
  • No more than ¼ inch thick, and flexible.
  • Rectangular, with the length at least 1.3 times the height. Square envelopes pay an extra nonmachinable charge.

Anything bigger, up to 12 × 15 inches, is mailed as a large envelope (“flat”) at a higher price. Rules and prices change, so check usps.com before a big mailing.

Measuring an envelope

Measure the envelope flat, with the flap closed: width first along the opening, then height. A ruler on your screen works for small envelopes once calibrated. To convert sizes, use inches to cm.

Frequently asked questions

What size is a #10 envelope?

4⅛ × 9½ inches (105 × 241 mm). It's the standard US business envelope, made to hold a sheet of US Letter paper folded in thirds.

What size envelope for a 5×7 card?

An A7 envelope, 5¼ × 7¼ inches. Envelopes are made about ¼ inch larger than the card in each direction, so a 5 × 7 card slides in easily.

What envelope fits an A4 sheet?

C4 (229 × 324 mm) holds A4 flat, C5 holds A4 folded in half, and DL (110 × 220 mm) holds A4 folded in thirds. In the US, a 9 × 12 inch envelope also takes A4 flat.

What is the largest envelope I can mail with one stamp?

For USPS letter rates, the envelope can be up to 6⅛ × 11½ inches and ¼ inch thick, and at least 3½ × 5 inches. Larger envelopes are 'flats' and cost more, and square or rigid envelopes pay a nonmachinable surcharge.

More measuring guides