Why does the Postal Service have minimum size standards?
We cannot effectively process mail smaller than our minimum size standards without causing damage to mail processing equipment, other mail pieces, and/or the small mail pieces themselves. Pieces that are smaller than our minimum size standards tend to be unstable when processed on mechanized and automated mail sorting equipment. As a result, these pieces get caught in mail processing equipment and damage the equipment as, well as other mail pieces. Their small size makes them difficult to handle manually also. In order to be mailable a piece must be at least be rectangular in shape, at least 3 1/2 inches high, 5 inches long (5 1/2 inches for international mail), and at least .007 inch thick (about the thickness of a postal card). Mail pieces not meeting these standards are returned to sender – usually under separate cover in a larger Postal Service envelop, with postage due charged to the mailer for the handling costs involved.
