MAILPIECE DESIGN
LETTERS
Letter size mail is mail that is 4 1/4 inches high or more than 6 inches long and must not be thinner than .007 inches thick.
POSTCARDS
Postcards are simply just a single layer of cardstock, cut to size. The maximum size is 4 1/4 x 6 inches. Anything larger than this size will qualify for letter rates.
Letter size mail is mail that is 4 1/4 inches high or more than 6 inches long and must not be thinner than .007 inches thick.
POSTCARDS
Postcards are simply just a single layer of cardstock, cut to size. The maximum size is 4 1/4 x 6 inches. Anything larger than this size will qualify for letter rates.

Downloadable PDF: Printable Letter-Size Mail Dimensional Standards Template. Note: Print actual size on an 11x14, legal size paper.
Avoid glossy stock for letters and postcards on automated mailings.
FLATS
Flats are larger mailpieces that exceed the maximum requirements for letters. Automation flats cannot weigh more than 13 oz. and must be rectangular. Thickness must not exceed 3/4 inches.
Flats are larger mailpieces that exceed the maximum requirements for letters. Automation flats cannot weigh more than 13 oz. and must be rectangular. Thickness must not exceed 3/4 inches.
The length of a flat piece is the longest dimension. The height is perpendicular to the length.
Flats must be flexible and universally thick. If a piece cannot bend without breaking it is not considered a flat. If the piece has more than 1/4 inch variedness in thickness, it is not considered a flat.
Flats must be flexible and universally thick. If a piece cannot bend without breaking it is not considered a flat. If the piece has more than 1/4 inch variedness in thickness, it is not considered a flat.
FOLDED MAILERS
Folded self mailers and booklets must be tabbed to prevent the open edges from causing delays in the high-speed automation process. It is important that when you are designing a folded mailer that the fold is on the bottom of the mailer such as seen in the graphic below.
Folded self mailers and booklets must be tabbed to prevent the open edges from causing delays in the high-speed automation process. It is important that when you are designing a folded mailer that the fold is on the bottom of the mailer such as seen in the graphic below.
If you have any questions about mailpiece design, please contact one of our mail specialists. This will help ensure that your pieces are designed for automation so you may recieve maximum discounts and to avoid USPS surcharges.