Physical Standards for Letters

Dimensional Standards for Letters

 Letter-size mail is the following:

1. Not less than 5 inches long, 3-1/2 inches high, and 0.007-inch thick. For pieces more than 6 inches long or 4-1/4 inches high, the minimum thickness is 0.009. (Pieces not meeting the 0.009 thickness are subject to a nonmachinable surcharge under 1.2f.)
2. Not more than 11-1/2 inches long, or more than 6-1/8 inches high, or more than 1/4-inch thick.
3. Not more than 3.5 ounces. (Charge flat-size prices for First-Class Mail letter-size pieces over 3.5 ounces.)
4. Rectangular, with four square corners and parallel opposite sides. Letter-size, card-type mailpieces made of cardstock may have finished corners that do not exceed a radius of 0.125 inch (1/8 inch).

Physical Standards for Flats

General Definition of Flat-Size Mail

Flat-size mail must have the following characteristics: 

a. Be more than 11-1/2 inches long, or more than 6-1/8 inches high, or more than 1/4 inch thick, other than automation flats under 6.0 or as allowed for USPS Marketing Mail pieces with simplified addresses under 5.2.2. 

Mailpieces other than automation flats or USPS Marketing Mail pieces with simplified addresses that are 1/4 inch thick or less must be at least 3-1/2 inches high and at least 5 inches long and be at least 0.007 inch thick.

b. Be not more than 15 inches long or more than 12 inches high or more than 3/4 inch thick, except for:

1.  Periodicals nonmachinable flat-size pieces mailed as specified in 207.26.0. They must not be more than 1-1/4 inches thick.

2. Polywrapped flats, with selvage that extends beyond the contents, up to a maximum length of 15-3/4 inches or a maximum height of 12-1/2 inches (see 4.5.4). The enclosed contents must not be longer than 15 inches or higher than 12 inches.

3. Co-mailed polywrapped flats mailed as specified in Customer Support Ruling PS-346, with selvage that extends beyond the contents, up to a maximum height of 12-7/8 inches (see 4.5.4). The enclosed contents must not be higher than 12 inches.

c. Be rectangular with four square corners or with finished corners that do not exceed a radius of 0.125 inch (1/8 inch) unless prepared as Customized Market Mail under 9.0. See Exhibit 1.1.1.

d. Other size or weight standards may apply to mail addressed to certain APOs and FPOs, and mail sent by the Department of State to U.S. government personnel abroad.