What size should I use for a direct mail piece?

Well, the truth is that there is no one answer to this question. However, the USPS does have size requirements that will determine which rates you will pay, so knowing the difference between a postcard, a letter size, and a flat size will help you to plan on how much it will cost you to mail your direct mail piece. Sizes are determined by the final dimensions after folding if necessary.

What is a Postcard size?

Postcard and double postcard sizes are restricted to the following:

  • Pieces must be rectangular in shape

  • Minimum dimensions are no less than 3.5 inches high and 5 inches long with a minimum thickness of 0.007 inches

  • Maximum dimensions are no more than 4.25 high or more than 6 inches long with a maximum thickness of 0.016 inches

  • Maximum weight 3.5 ounces

 

* As of August 29th 2021 the USPS changed their maximum dimensions for presorted and automation First Class postcard pieces. Pieces processed in these categories can have a maximum dimension up to 6 inches high by 9 inches long, however the minimum thickness for these pieces will be 0.009 inches for pieces that exceed the 4.25 x 6 inch dimensions.

Postage rates for presorted and automation postcards range from $0.306 each to $0.326 each and receive first class handing by the post office, so you may see faster delivery as compared to Standard rate mail.

What is a Letter size?

Letter sizes are restricted to the following to avoid non-machinable surcharges:

  • Pieces must be rectangular in shape

  • Minimum dimensions are no less than 3.5 inches high and 5 inches long and 0.007 inches minimum thickness. For pieces more than 4.25 high or more than 6 inches long the minimum thickness is 0.009 inches. Notice that there is some overlap with the postcard sizes. If you are doing a card mailer you can choose to mail it as a postcard with first class treatment or as a letter with standard mail treatment. Non-card letter or folded self-mailers can also be mailed at First Class or Standard rates but must comply with the minimum & maximum letter size requirements.

  • Maximum dimensions are no more than 6.125 inches high or more than 11.5 inches long with a maximum thickness of 0.25 inches. Folded self-mailers have a maximum length of 10.5". Folded self-mailers are formed of two or more panels that are created when one or more unbound sheets of paper for folded together and sealed to make a letter-size piece.

  • Maximum weight 3.5 ounces

  • Aspect ratio between 1.3 to 2.5 inclusive. The aspect ratio is the length divided by the height. For example a piece 5 inches high by 7 inches wide would have an aspect ratio of 1.4

Postage rates for First Class presorted and automation letters range from $0.426 each to $0.485 each.

 

Postage rates for Standard rate presorted and automation letters range from $0.172 each for Saturation SCF entry to $0.33 each for None entry Mixed. These receive 3rd class handing by the post office, although for local pieces most of the time they are processed in about the same amount of time as First Class pieces but there is no guarantee of that.

What is a Flat size?

Flat sizes are pieces that have one dimension that exceeds the letter size dimensions and thickness requirements such as large envelopes, newsletters and magazines.​

  • Height exceeds 6.125 inches or Length exceeds 11.5 inches or thickness exceeds 0.25 inches.

  • Maximum dimensions are 12 inches high or 15 inches in length with a maximum thickness of 0.75 inches. Pieces that exceed these dimension may be mailable but not as Flats.

  • Maximum weight 13 ounces. Pieces up to 4 ounces have a per piece rate. Pieces over 4 ounces up to 13 ounces are charged a price per pound plus a per piece amount.

Postage rates for First Class presorted and automation flats are charged by the ounce. For up to 1 ounce the postage will range from $0.555 each to $1.00 each with and additional $0.20 per piece per ounce up to 13 ounces.

 

Postage rates for Standard rate presorted and automation flats up to 4 ounces range from $0.188 each for Saturation SCF entry to $0.332 each for None entry Mixed. These receive 3rd class handing by the post office. Most of the time flats take a bit longer for processing that letters.