Postcard Stamp Size Guide with Rates, Rules and Placement

Here is the part most people get backwards. The physical size of the postage stamp on your postcard does not matter at all. What matters is whether the card itself qualifies for the cheaper USPS postcard-rate stamp or gets bumped up to the pricier First-Class letter rate. That gap looks tiny on one card and turns into real money the moment you are mailing hundreds or thousands.

This postcard stamp size guide walks through the exact USPS dimensions your card has to hit, what happens the second you go oversized, and how to keep your postage as low as the rules allow. Whether you are running a direct mail campaign, sending appointment reminders, or mailing event invitations, getting the size right protects your budget. 4OVER4.COM prints standard postcards across a catalog of 1,000-plus products, all built to meet postal standards.

Working on the rest of the campaign too? Our guide on how to fold a brochure covers folding, how to clean rubber stamps keeps your return-address stamp crisp, and how to make postcards takes you from blank file to finished mailer. Want to start designing now? Browse the 4OVER4.COM design templates for ready-to-use layouts.

Most printed postcards land in a handful of common sizes, and not all of them earn the postcard rate. Here is what to expect from each one that does.

4" x 6" postcards are the most popular size for direct mail. They sit comfortably inside the USPS postcard window at 4 inches tall and 6 inches long, which makes them the default for marketing campaigns, appointment reminders, and event announcements. A single postcard-rate stamp in the upper right corner is all they need.

3.5" x 5" postcards hit the minimum size. They are compact, cost-effective, and well suited to thank-you notes, save-the-dates, and quick promos, and they still qualify for the postcard rate. 4.25" x 5.5" postcards sit right at the maximum height while staying inside the allowed range, so they give you a little more design room without crossing into letter territory. For a deeper look at every format, see our postcard sizes and dimensions guide.

Stamp placement is not just tradition, it is a USPS requirement. The stamp goes in the upper right corner of the address side of the card. That placement is non-negotiable if you want your mail processed by automated sorting equipment rather than pulled for manual handling.

USPS sorters scan the upper right area for postage, so a stamp in the wrong spot can get your postcard delayed, returned, or hit with extra handling fees. Here is how the address side needs to be laid out:

• Stamp area: upper right corner, with clearance from the edge.
• Return address: upper left corner.
• Recipient address: center-right area, at least 5/8 inch up from the bottom edge.
• Barcode clear zone: the bottom 5/8 inch stays blank for postal barcodes.

The left half of the address side can carry a short message or a bit of branding, but keep the right half clean for the address and postage. A scannable QR code on your postcard fits neatly in that message space, and our guide hub has dozens more print and mail walkthroughs.

Sending postcards one at a time? A postcard-rate stamp works fine. Once you are mailing 200 or more identical pieces, though, you have better options than sticking stamps by hand.

USPS Marketing Mail, formerly Standard Mail, offers discounted rates for bulk mailings of 200-plus identical pieces. Depending on how you sort and prepare the batch, rates can drop to around $0.30 to $0.40 per piece. You will not use individual stamps for these, you will use a permit imprint or metered postage instead. To qualify, your postcards still have to meet the standard size rules, and you sort by ZIP code and drop the batch at a Business Mail Entry Unit.

For smaller runs, precanceled stamps or meter strips speed things up, and online postage services like Stamps.com or Pitney Bowes can print postage straight onto the card or a label. Mailing to entire neighborhoods? Our EDDM guidelines cover Every Door Direct Mail setup, and direct mail postcards arrive ready for your list. Want another keepsake format to add to the drop? See our custom magnets guide.

Even seasoned mailers slip up. These are the errors that lead to returned mail, surcharges, and delays, along with how to sidestep each one.

• Designing at 4.5" x 6.25" and calling it close enough. It is not. Even a fraction of an inch over 4.25" x 6" bumps the card to letter rate, so always design to the exact finished trim size.
• Using ultra-thick paper for mailed cards. That gorgeous 32pt stock exceeds the 0.016-inch maximum. Save it for hand-delivered pieces.
• Putting the stamp on the wrong side. The stamp belongs on the address side, upper right corner. It is easy to lose track of which side is which while you design the front.
• Forgetting the barcode clear zone. The bottom 5/8 inch of the address side must stay blank. Text or dark backgrounds there cause processing errors.
• Assuming every square card gets the postcard rate. Square mail pieces always pick up a non-machinable surcharge, so stick to rectangular formats.

4OVER4.COM builds every standard postcard template to USPS mailing specs, so you start with the right dimensions instead of correcting them later. Comparing print shops first? Our best postcard printing services compared guide lays out the options.