Guide · Updated
Postcard sizes and USPS mailing requirements, explained
We print two direct mail postcard sizes, 5×8.25 and 6×11, and this guide explains why: how each USPS size class mails, the rules on dimensions, thickness, address placement and clear zones, and how to set up a file that mails at the lowest rate.
Postcard size decides two things: how much room you have and what the postage costs. The USPS charges by size class, not by inch, so a card a fraction of an inch too big for the postcard class pays the letter rate, and a 6×11 gives you a third more room than a 6×9 for the same letter postage. This guide lays out the size classes, the class each size mails at, the mechanical rules that make a card mailable, and why our two sizes, 5×8.25 and 6×11, cover almost every job.
Common postcard sizes and how they mail
| Size | USPS class | Best for |
|---|---|---|
| 4×6 (up to 4.25×6) | First-Class postcard or Marketing Mail letter | Reminders, follow-ups; small |
| 5×8.25 (ours) | Letter | Offers with a photo, a map and details; farming cards |
| 6×9 | Letter | A middle size; less room than the 6×11 for the same postage |
| 6×11 (ours) | Letter | Jumbo cards for real estate, home services, restaurants, neighborhood saturation |
| 8.5×11 | Flat | Full-page flats; more paper than most offers need |
Why 5×8.25 and 6×11
Two sizes cover almost every direct mail job. The 5×8.25 mails as a letter-size piece to a list at the same Marketing Mail postage as any card up to 6.125×11.5, so it carries a photo, an offer, a map and a QR code for the least print. The 6×11 is the largest card that still mails at letter rates, so it gets the most room for the least postage, and it is the card we suggest when a whole neighborhood is getting one. Running two formats on repeat instead of a dozen keeps setup short and waste low, which shows up in the quote.
The USPS size classes
A postcard for the First-Class postcard rate must be at least 3.5×5 and no larger than 4.25×6, between 0.007 and 0.016 inch thick. A letter-size piece is anything up to 6.125×11.5 and 0.25 inch thick, up to 3.5 ounces for Marketing Mail; both of our sizes mail as letters to a list. A flat is anything larger than letter size up to 12×15 and 0.75 inch thick. Pieces must be rectangular, and a letter-size piece's aspect ratio (length divided by height) must be between 1.3 and 2.5 to run on automation equipment, which both of our sizes satisfy.
Address side layout and clear zones
The address side has to leave room for the machines. The address block sits in the right half (or the OCR read area) with the delivery address and ZIP+4; the bottom 0.625 inch of the piece must be clear across its full width for the Intelligent Mail barcode; the indicia or stamp sits in the upper right corner; and nothing else, no color blocks, no photos, no text, should sit inside those zones. Our templates draw the zones for both sizes, and the preflight flags anything inside them.
- Address block: right half, left-aligned, 8pt or larger, no reversed type
- Barcode clear zone: bottom 0.625" full width
- Indicia: upper right, sized per our template
- Return address: upper left, optional but recommended
- Message and art: the left half of the address side and all of the front
Paper, thickness and coating
Postcards mail well on 14pt or 16pt cover (about 0.014 to 0.016 inch), which meets the USPS minimum thickness for every class and survives handling. Thinner stocks bend in the sorter and can be charged at a higher rate for non-machinability. Gloss UV coating is fine on the front and on the non-address areas of the back, but the address block and barcode area must accept ink from the USPS sprayers, which is why we leave the address area uncoated or use an aqueous coating that takes ink. Very dark backgrounds behind the address are a common cause of unreadable barcodes.
Setting up the file
Export a PDF at 300 dpi in CMYK with 0.125 inch of bleed on every side and text at least 0.1875 inch inside the trim. Set the document to the finished size plus bleed (a 6×11 is 6.25×11.25 with bleed; a 5×8.25 is 5.25×8.5). Embed or outline fonts. Keep QR codes at least 0.75 inch square with quiet space around them. Place the address block and clear zones per the template for your size. If you would rather not build the file at all, we design the card, and the free preflight checks either one before the job prints.
Once the size is settled, the price of printing and mailing it is explained in how much direct mail costs.
Sources
Answers
Questions this guide answers
What is the standard size for a direct mail postcard?
Jumbo cards around 6×11 are the standard for marketing postcards, and a mid-size card like our 5×8.25 is the standard for offers and farming. We print those two sizes; both mail at Marketing Mail letter rates, to your list or to whole neighborhoods.
What is the largest postcard size that mails at the letter rate?
6.125×11.5 inches and 0.25 inch thick. A 6×11 postcard is the largest standard size under that limit, which is why it is the go-to jumbo card.
What is the cheapest postcard size to mail?
Mailed as USPS Marketing Mail, every size up to 6.125×11.5 pays the same letter postage, so the 6×11 is the best value per square inch and the 5×8.25 the least print for a full message. Only a card no larger than 4.25×6 qualifies for the First-Class postcard rate.
How thick should a postcard be?
The USPS minimum is 0.007 inch for cards up to 4.25×6 and 0.009 inch for larger letter-size pieces. We print on 14pt (about 0.014 inch) or 16pt cover, which is well over the minimum and feels substantial in the hand.