The contents, weight, size, and design of your mailpiece will determine the category (e.g., letters, cards, and flats) and class of mail. First-Class Mail may weigh up to 13 ounces. USPS Marketing Mail, including Nonprofit USPS Marketing Mail, must weigh less than 16 ounces.
Various presort discounts apply to both First-Class Mail and USPS Marketing Mail. Additional discounts are available for automation pieces, provided the mailpiece meets the applicable automation compatibility requirements. For further information, see DMM 201.3.0 (cards/letters) at https://pe.usps.gov/text/dmm300/201.htm#ep1042622 and 201.6.0 (flats) at https://pe.usps.gov/text/dmm300/201.htm#ep1097107.
