Standard-size Mail Dimensions
for the United States Postal Service

Minimum and maximum sizes (and other requirements) to qualify for USPS letter and postcard rates. Contact a USPS Mailpiece Design Analyst for assistance.

Postcards

1. Minimum Size: 3.5 x 5"
2. Maximum Size: 4.25 x 6"
3. Thickness: at least 0.007" thick but not more than 0.25" thick. This means use cardstock.
4. Flexibility: Must not be rigid. Must be at least as flexible as a credit card piece.
5. Aspect Ratio: The aspect ratio (length divided by width) must fall between 1 : 1.3   to  1 : 2.5
   
   (Using the template below, place the lower left-hand corner of the piece where indicated. The upper right-hand tip of your piece must fall within the shaded area--and be within the size requirements.)

Letter-size Pieces

1. Minimum Size: 3.5 x 5"
2. Maximum Size: 6.125 x 11.5"
3. Thickness: at least 0.007" thick but not more than 0.25" thick. This means the piece must fold, or you must use cardstock or you must use an envelope.
4. Flexibility: Must not be rigid. Must be at least as flexible as a credit card piece.
5. Aspect Ratio: The aspect ratio (length divided by width) must fall between 1 : 1.3   to  1 : 2.5
   
   (Using the template below, place the lower left-hand corner of the piece where indicated. The upper right-hand tip of your piece must fall within the shaded area.)

Pieces such as keys and ID devices are not subject to minimum standards except for the thickness rule.

Machinability Standards for Folded Self-Mailing Pieces

1. Trifold preferred over bi-fold
2. Fold on the bottom.
3. Sealing or tabbing required.
4. No Staples
   
   (Using the template below, place the lower left-hand corner of the piece where indicated. The upper right-hand tip of your piece must fall within the shaded area.)

Letter-size Mail Dimensional Standards Template