Can I Use Package Services to Send Flats with USPS?

Flats need to be mailed with the United States Postal Service, and not shipped
ship flats with USPS

A lot of people ask us whether or not they can ship flats with USPS. Technically, the answer is no. While you can send flats with the Postal Service through the mail, you can’t use any of USPS’ shipping services such as First Class Package Service. Sorry!

What Does USPS Classify as Flats?

“Flats” refer to large envelopes, newsletters, and magazines. In fact, USPS uses the phrases “large envelopes” and “flats” interchangeably to describe the same thing. A good example to think of are those manila folders that you see in the above photo.

According to USPS’ website, flats must:

  • Have at least one dimension greater than 6.125 inches high, 11.5 inches long, or 0.25 inches thick
  • Have maximum dimensions no more than 12 inches high, 15 inches long, and 0.75 inches thick

Here’s what it all comes down to. If you want to use First Class Package Service instead of First Class Mail Flats, your package needs to be rigid, lumpy, and/or most importantly, thicker than 0.25 inches.

Pro Tip: Don’t confuse flats with Priority Mail Flat Rate boxes or envelopes! They are two entirely different things, and require different types of postage.

Large Envelopes Technically Need to Be Mailed, Not Shipped

Since USPS clumps flats and large envelopes into their regular mail stream, flats don’t come with tracking numbers automatically. If you’re sending sensitive documents and would like to be able to track them, we suggest purchasing Certified Mail service for your flats. Certified Mail is a mail service a tier above First-Class Mail that assigns a tracking number to your envelope.

Keep in mind that if you purchase a shipping service such as First Class Package for an envelope that looks like a flat, USPS may return it back to you. You’re better off just sticking with regular First Class Mail or Certified Mail.

Learn more about the difference between mailing and shipping.

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