First Class “Flats”

The Postal Service uses the word “flats” to refer to large envelopes, newsletters and magazines.

Weights and Sizes

To qualify as a first class flat, envelopes must:

  • Have one dimension that is greater than 6-1/8 inches high OR 11-1/2 inches long OR 1/4 inch thick
  • Be no more than 12 inches high x 15 inches long x 3/4 inch thick (for a copy of the Flats Design template, click here: 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 price – 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 price (see more information on First Class Letters here)


Tips for shipping flats-

  • The font and writing of the address should be proportional to the size of the envelope for easy reading. Don’t use tiny fonts on a large envelope because they won’t be caught as easily.
  • If the envelope is not bendable because it contains a key, a cd, a book, cardboard, photographs etc… it will be charged a “non-machinable” surcharge and bumped up in class to a parcel.
  • If you use the manila envelopes with brad enclosures, please tape over the metal. Sometimes (not always) the metal can catch on the postage machine and rip the envelope 🙁