FLATS (USPS)

The Postal Service uses the words "flats" and "nonletters" to refer to large envelopes, newsletters, and magazines. The words are interchangeable. Whatever you call them, flats must:

★ Have one dimension that is greater than 6-1/8 inches high OR 11-½ inches long (the side parallel to the address as read) OR ¼ inch thick.

★ Be no more than 12 inches high x 15 inches long x ¾ inch thick.

NOTE:
This general rule does not apply to:

★ Automation rate flats.

★ Standard Mail Enhanced Carrier Route flats.
The maximum size for a flat provides plenty of room to put lots of material in the envelope. But keep in mind that weight (usually affects rate) – the higher the weight the higher the postage, especially for First-Class Mail.
Is it possible to fold your flat-size piece to letter-size? If so, you can save money because you'll pay the lower letter rate.

Contents

External links and references

External links and references

★ USPS page on flats