Visit the USPS Price List page for current postage and shipping rates.
To qualify for mailing at the First-Class Mail postcard price, it must be:
- At least 3½ inches high x 5 inches long x 0.007 inch thick
- No more than 4¼ inches high x 6 inches long x 0.016 inches thick
If your mail piece does not meet the dimensions above, then the Postal Service considers it a letter. Letter-size postage will be charged.
To be eligible for mailing at the price for letters, a letter must be:
- At least 3½ inches high x 5 inches long x 0.007 inch thick.
- No more than 6⅛ inches high x 11½ inches long x ¼ inch thick.
First-Class Mail letters that have one or more non-machinable characteristics will pay a non-machinable surcharge. Customers can be unpleasantly surprised that they must pay extra postage when, for example, they mail a square greeting card. The Postal Service charges extra postage because mail pieces that are rigid, square, or unusually shaped, often jam postal equipment and are difficult to process. For a list of non-machinable characteristics, download the non-machinable characteristics (PDF) document.
Examples of a non-machinable letter:
- A letter that has an aspect ratio (length divided by height) of less than 1⅓ or more than 2½ (a square envelope has an aspect ratio of 1, making it non-machinable).
- A letter that is more than 4¼ inches high or 6 inches long and is less than 0.009 inch thick.
- A letter that has clasps, strings, buttons, or similar closure devices.
- A letter that is too rigid.
- A letter that has a delivery address parallel to the shorter side of the mail piece.
- A letter that contains items such as pens, pencils, or keys that create an uneven thickness.
Large Envelopes and Flats
The Postal Service uses the word “flats” to refer to large envelopes, newsletters, and magazines. The words large envelopes and flats are used interchangeably.
- Have one dimension that is greater than 6⅛ inches high OR 11½ inches long OR ¼ inch thick.
- Be no more than 12 inches high x 15 inches long x ¾ inch thick.
* Large Envelopes exceed one or more of the letter size maximum dimensions.
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 price– the higher the weight the higher the postage, especially for First-Class Mail.