When we talk about mail piece design with clients, it’s usually in the context of driving response. Successful direct marketers balance the cost of various aspects of mail piece design with the changes that design elements can drive in response rates. However, one factor in that cost calculation can be overlooked: The impact of design decisions on postage spend.


The three biggest drivers of postage cost are mail class, piece shape, and piece weight.

Mail Class: Admittedly, mail class isn’t really a design issue, but as you will see, class can have an impact on things that are design issues. And mail class is definitely something to think about regarding postage cost. First-Class Mail (FCM) is the premier service for the U.S. Postal Service (USPS) and comes with faster delivery and lots of built-in services (like forwarding and return to sender). But those services come with a cost. If all you need is to get your marketing piece in the recipient’s hands in a specific date window and you aren’t using the extra services, Standard Mail (now also known as Marketing Mail) may be a more cost-efficient way to have your mail piece delivered.

Piece Shape: What you or I may simply refer to as the size of a mail piece, the Postal Service refers to as “shape.” The most efficient shape for the USPS to process is letters; mail pieces that are between 3.5” x 5” and 6.125” x 11.5” and no more than 0.25” thick. Once a piece exceeds one of the maximum dimensions, it becomes a flat, which can drive up postage cost at least 30% for Standard/Marketing Mail and at least 20% for FCM.

If your current control package is a flat, consider testing slightly smaller designs, which can save significant postage while driving similar response rates to your larger control package. My colleagues have found that “stretch” packages (about 6” x 11”) are large enough to garner extra attention in the mailbox while still qualifying for lower letter postage rates.

One design-related difference to keep in mind related to letters and flats is the address on a letter-shaped piece must be parallel to the longer dimension of the mail piece, while the address on a flat-shaped piece can be parallel to either the longer or shorter dimension.

Piece Weight: The weight of a mail piece has traditionally been an important driver of postage cost, especially for FCM. However, with the new postage rates that took effect January 22, that is much less the case.

In recent years, commercial FCM, which used to be charged strictly by the ounce, has had a feature called “Second Ounce Free,” which meant mail pieces weighing less than two ounces could be mailed at the one-ounce rate. That program proved popular enough that the Postal Service has opted to make FCM pricing even simpler. Since January 22 , all commercial FCM Letters up to 3.5 ounces are charged the one-ounce price! (Caution: you must be using presort or automation rates to avail yourself of this feature. FCM single-piece rates are still structured around ounce break points.)

Standard/Marketing Mail has also seen simplification in weight-based pricing. The piece rate now applies to all enveloped letters up to a weight of 3.5 ounces and flats up to four ounces. Above these weights, a piece/pound calculation takes over and adds cost.

An added benefit is that the break point for both FCM and Standard letters is now 3.5 ounces before additional postage costs take effect ― only one number to remember!


No matter which class, shape, or weight mail piece you use, one of the most important ways to control postage cost is to ensure the mail piece meets all the requirements to claim automation discounts.

Enveloped letters, in addition to meeting the size constraints noted above, must also be designed within a few other parameters.

· Piece weight can be no heavier than 3.5 ounces.

· Pieces must have an aspect ratio (length divided by height) of 1.3 to 2.5. This means all those perfectly square designs that may get your creative team excited are going to cost more to mail.

· The Intelligent Mail barcode (IMb) must fall at least 0.625” but no more than four inches from the bottom of the mail piece. It can also be no closer than 0.5” to either left or right edge of the mail piece.

· The piece must be flexible enough to be handled by automated sorting equipment. The official definition is “bend easily when subjected to a transport belt tension of 40 pounds around an 11-inch-diameter drum.” Not a measurement that slides gracefully off the tongue. The way I think of it is promotional plastic and paper cards work; anything heavier or stiffer (seed packets, pens, and other rigid and odd-shaped items) are generally prohibited.

Automation requirements for flats aren’t as strict because the sorting machines are designed to handle bigger, bulkier pieces (think catalogs and magazines). Piece size can be no larger than 12” x 15” and no thicker than 0.75”. Additional design features to note:

· Piece weight can be no heavier than 13 ounces (FCM) or 16 ounces (Standard/Marketing Mail).

· There is no aspect ratio requirement.

· IMb placement can be anywhere so long as it is at least 0.125” from any edge.

· Flexibility requirements are less stringent than for letters, so some of those stiff inserts that don’t work in automation letters will work in automation flats.

· But do be careful, flats need to pass the “droop test.” Large, very lightweight mail pieces can be too flimsy for sorting machines to handle. A full explanation of how mail piece deflection is measured is available in DMM 201.4.6.


Our discussion so far, at least relative to letters, has focused on enveloped mail pieces. If you are looking at folded self-mailer designs, the rules are a bit different. The USPS definition of a folded self-mailer is “two or more panels that are created when one or more unbound sheets of paper are folded together and sealed to make a letter-size mail piece.” For these types of mail pieces, maximum piece size is 6” x 10.5” and maximum weight is three ounces ― both measurements slightly less than the maximums for enveloped mail pieces.

Folded self-mailers also require specific:

· Minimums for paper weight based on piece design;

· Tabbing or gluing patterns for piece closure based on piece weight and design;

· Size requirements for flaps (if used); and

· Number and orientation of folded panels.

For more details on folded self-mailers, consult the Folded Self Mailer Reference on the USPS RIBBS website (https://ribbs.usps.gov/fsm/documents/tech_guides/FSMReference.pdf).

The right design decisions not only drive strong direct mail response rates; they can also ensure you aren’t paying unnecessarily high postage rates. Be sure to think about the postage impact the next time you’re trying to determine the best creative design for your direct mail campaign.

Kurt Ruppel is Director Postal Policy and Marketing Communications at IWCO Direct. He is a member of the Mailers’ Technical Advisory Committee (MTAC) and serves on the Board of Directors at the Envelope Manufacturers Association (EMA), where he is also Vice Chair of the EMA’s Postal Affairs Committee. He can be reached at kurt.ruppel@iwco.com.