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Authorized Envelopes

Please Note: Failure to comply explicitly with USPS rules may cause your mail to be REJECTED.

Below are the dimensions of postcards, letters and flats that are authorized by the USPS. All outgoing University mail is to stay within these dimensions. Addressing on these envelopes is always to be parallel to the longest side of the envelope. Addressing them on the short side is considered non-machinable. Violations of this rule costs the University additional postage fees for each piece and may slow down delivery.


  • Postcards are a flat, single piece of hard (cardboard like) paper with no folds. The following are the dimensions of a legal postcard. Anything else would be a First Class letter or a Flat, depending on size, weight and thickness

First Class Letters

  • First Class Letters are to be sent using a #10 envelope, which is a standard business mailing envelope (9 ½" x 4"). If the amount of paper in the envelope causes it to be thicker than 1/4 of an inch, then a standard 6" x 9" envelope should be used. This will allow the paper to be folded only once and save on the thickness issue.
  • The USPS standards for first class envelopes are listed below. Anything beyond these dimensions is considered a Flat or a Parcel. Cost rises considerably when going outside these dimensions. If a regular #10 mailing envelope is over 1/4 inch thick, it becomes a very costly flat. If you have a number of pages that must go in a #10 envelope, using a 6" by 9" envelope may keep it classified as a Letter and not a Flat.



  • Flats should only be used to send large promotional materials that will not fit in a standard mailing envelope. Anything larger than the dimensions listed below is considered a parcel. Placing letters or single sheets of paper into large envelopes is not acceptable and very wasteful.