Following USPS® design guide will ensure your mail will be accepted without problem and will get the maximum possible postage discount.

Even though to design for direct mail is not a lot different from creating any other print ready design, there are simple rules and guidelines one should follow in order to maximize the available postage discount. You can download the latest postal rates from our resource page under the current postal rates tab.

The postal rules and manuals can be frustrating and hard to understand.

So, here is a very easy “how to” guide to help you pick the right size, design and prepare for maximum postage savings.

In order to qualify for the maximum postage discount your mailipiece must be automation compatible. First component which plays major role in the said qualification is the physical attributes of the mailpiece, or in other words the piece you intend to send out must comply with the USPS® regulations for the physical standards for automation letters, flats or postcards.


Generally USPS® marketing mail, prevously known as “standard mail” or “bulk mail”, has two major size groups LETTERS and FLATS and one, I will call it “special” group - POSTCARDS. I agree that the names are pretty misleading, that is the reason sometimes is hard to explain to the marketers that a postcard 9" x 6" is actually a LETTER-size mailpiece. By the way all the rules for physical dimensions are exactly the same whether you mail at first-class, marketing (standard) mail or non-profit rates.


Second component to be considered is the addressing and barcode. How to address and apply the barcode is responsibility of your mailing house, but in order for them to comply you need to do the design with the precise size and placement of the space for the address block and imprint the right indicia (permit). 



Letter-Size Mailpiece

For a mailpiece to be automation compatible and consider for the letter-size postage discounts it must be:

- rectangular in shape

- minimum 3 1/2" and maximum 6 1/8" high

- minimum 5" and maximum 11 1/2" long

(see diagram)

- piece has to be minimum 0.007" thick and not more than 0.25" - which means for a single sheet piece, use at least 8pt cover stock, but to be safe, because specs and measures vary between manufactures, I would always recommend to use minimum 10pt cover stock

- aspect ratio (very common mistake!) between 1.3 and 2.5. Aspect ratio is the length divided by the height. Example: 6"x 9" piece ratio is 9/6=1.5, which is within the limits. Any piece out of the standard aspect ratio are subject to a pretty hefty surcharge, so unless is absolutely necessary keep the ratio good!

-  automation compatible letter-size mailpiece must weigh maximum 3oz if single sheet or up to 3.5 oz if envelope with inserts.

Additional standards: no polly or shrink bags or wraps, no clasp, strings, buttons or similar closure items that can damage the processing equipment.

Enclosed items cannot be rigid, odd shaped. Only firmly affixed flexible items are permitted like gift or credit cards. The content must bend easily.

The addressing side cannot be glossy or with any type of coating.

Letter-Size Mail Dimensional Standards Template

SELFMAILERS and multiple page pieces (booklets and catalogs) in order to be automations compatible must be closed with tabs. Rules for the tabs are a bit complicated so I strongly advise to ask your mailing house before you finalize your layout.



As I mentioned before Postcard as a mailpiece is special and unique. It’s limited in sizes and refer only to a piece mailed at First-class also known as postcard rate. “Postcard” mailed at standard rates is a Letter-size mailpiece. 

- rectangular in shape

- minimum 3 1/2" and maximum 4 1/4" high

- minimum 5" and maximum 6" long

(see diagram)

- piece has to be as low as 0.009" thick and not over 0.016" - I always recommend one more time to use at least 10pt cover stock.

- aspect ratio between 1.3 and 2.5. Note: USPS are very strict when it comes to the size and aspect ratio of postcards. 

Additional standards: precise rules for addressing, messaging and clear zone, please see the diagram. 

The special first-class rate for postcards is almost the same as the standard rate. So if you consider mailing a 4"x6" card make it first-class, unless you are not mailing to a saturation mailing list.

Letter-size and Postcard Physical Standards


- rectangular in shape

- minimum 6 1/8" and maximum 12" high

- minimum 11 1/2" and maximum 15" long

(see diagram)

- piece has to be minimum 0.009" thick and not more than 0.75"

- automation compatible flat-size mailpiece must weigh maximum 13oz if mail first-class and up to 16oz if mailed at USPS® marketing (standard) mail rates.

Additional standards: Clasps, strings and similar are prohibited, but polly wraps are permitted only if certified by USPS® manufacturers are used.

Enclosed items has to be spread evenly inside the envelope. The content must bend easily.

Tyvek envelopes are not permitted, non-glossy stocks are recommended.

Flats Physical Standards

Addressing Rules

The standard address block of four lines plus barcode and optional OEL (optional endorsement line) takes about 3 1/2" x 1 1/2" space plus the absolute minimum of 1/8" clearance around the “white box” should be at least 3.75" x 1.75" and placed at least 1/2" from the right  and 5/8" from the bottom of the mailpiece. The rule also apply for the window envelopes. But that is not all ... even though there is some flexibility to fit within the OCR reading area, you have to look for the following:

- never put important information below the address block as that is the place where the post office may put some marks or white strip label

- never put the return address or any other address for that matter in the OCR area as the machine must misread the actual address

- the permit needs to be readable, at least 6-7pt and printed in black or if color - very dark

- the font for the address (if mailer ask for your choice) needs to be readable - avoid using script, narrow or heavy bold type, all upper case are preferable and at least 10pt in size and always larger than the return address.

- address lines have to be left justified, not centered

- for flats - delivery address has to be always to the right of the return address, no slightly under or below

Letter-size Addressing Template
Postcard Addressing Template
Flat mailpiece Addressing Template

I know that sometimes the rules and regulations seams like that don’t make sense, but believe they do! All the rules and restrictions in size, formats, etc are developed to enhance the process and reduce the undeliverable mail. Additional and detailed information about the mailpiece design and preparation can be found on USPS® website or you can always contact our direct mail specialist.

I really hope this simple guide will help with your future direct mail pieces design, but if you want to make sure everything is up to the USPS standards and to avoid unnecessary surcharges, contact us, we will be more than happy to help.

Following USPS® design guide will ensure you will get the maximum possible postage discount.
Milena Marguenski
Milena is the owner and CEO of US Presort.
US Presort | 3801 Victory Blvd., Suite 1 - Staten Island, NY 10314 | P : 718.980.6556