Flats (USPS)


The United States Postal Service uses the words "flats" and "nonletters" interchangeably to refer to large envelopes, newsletters, and magazines.

Size restrictions

To fit the definition a flat must:
Furthermore, the item must be somewhat bendable: see the USPS Domestic Mail Manual for exact details.
This general rule does not apply to: Automation rate flats and Standard Mail Enhanced Carrier Route flats.

Postage

The maximum size for a flat provides enough room to enclose much material. An issue, however, is that the higher the weight the higher the postage, especially for First-Class Mail.