USPS Postcard Guidelines & Mailing Regulations
Stay inside the postcard size window, lay out the address side correctly, and keep the barcode corner clear. Here are the USPS postcard rules in plain English, so your mailing qualifies for the lowest tier and moves through automation without surcharges.
To meet USPS postcard guidelines, keep the card rectangular between 3.5 by 5 inches and 4.25 by 6 inches, at 0.007 to 0.016 inches thick. Put postage top right, the return address top left, and the recipient address on the right half, and leave the lower right barcode clear zone empty. Stay in that window and your card qualifies for the postcard postage price. Go larger and it mails as a letter.
Quick tips
Quick tips for a USPS-compliant postcard
Keep your card between 3.5 by 5 and 4.25 by 6 inches to qualify for the postcard postage price. Put postage in the top right, the return address in the top left, and the recipient address on the right half of the address side. Leave the lower right barcode clear zone empty, use a stock 0.007 to 0.016 inches thick, and send a full-bleed, 300 DPI file. 4OVER4.COM postcards are built to hit these rules out of the box.
Why USPS postcard guidelines matter before you print
A postcard that ignores the USPS rules costs you twice: once when the post office charges a higher rate, and again when a rejected barcode delays the whole drop. Learning the guidelines first, before you design, keeps your mailing on the lowest postage tier and moving through automation without surcharges.
The rules are simpler than they look. There are three things the USPS cares about: the size of the card, the layout of the address side, and the stock it is printed on. Get those right and everything else is creative freedom. This guide walks through each one in plain English so you stop bouncing between technical bulletins.
Everything here applies to the postcards you can order from 4OVER4.COM, including direct mail postcards built for list drops and the full range at postcards printing. If you want us to print, address, and send the whole run, our direct mail services handle it end to end.
USPS postcard size requirements
The postcard price is a size class, not a shape you get to choose freely. To qualify, a card must be rectangular and sit inside this window:
- Minimum: 3.5 inches high by 5 inches long.
- Maximum: 4.25 inches high by 6 inches long.
- Thickness: 0.007 to 0.016 inches (roughly a sturdy card stock, not paper-thin and not board-thick).
The two most common sizes people order, 4 by 6 inches and 4.25 by 5.5 inches, both land safely inside that range. Go past 4.25 by 6 inches and the card is still mailable, but it prices as a First-Class letter rather than a postcard. That is the whole reason oversized postcards cost more to send: the extra real estate pushes them into a higher class.
One more rule that trips people up: the card has to be rectangular for the postcard price. Rounded corners are fine, but a die-cut postcard in a non-rectangular shape is treated as a nonmachinable letter and pays a surcharge. Design bold, just know the trade-off.
Postcard clear zones and the barcode area
Clear zones are the parts of the address side you leave empty so postal equipment can read and route the card. The one that matters most is the barcode clear zone in the lower right corner: about 4.75 inches wide and 0.625 inches tall. The USPS prints or scans the routing barcode there, so any design bleeding into that corner risks a rejected or hand-sorted piece.
Keep the message, logo, and imagery to the left half of the address side, or put them entirely on the reverse. If you are laying the card out yourself, the online designer at 4OVER4.COM keeps these zones visible so you do not accidentally print into them.
Address block placement and layout
The address side follows a fixed grammar. Once you know it, every mailer you design lines up the same way.
- Postage or indicia: top right corner. Whether you use stamps, a meter, or a permit imprint, this corner is reserved.
- Return address: top left corner, in a smaller type size than the delivery address.
- Recipient address: the lower right region, printed parallel to the longest edge, sitting just above the barcode clear zone.
Use a clean, machine-friendly font at a readable size for the delivery line, and keep the address block on a plain, light background. Reverse type (white on dark) and script fonts read poorly on postal scanners and can bump the piece to manual handling. If you are running a mailing list, our direct mail services place and format the address block for you so every card is automation-compatible.
The left half of the address side is still yours. A short offer, a call to action, or a QR code lives comfortably there without touching any clear zone.
Postcard postage rates and savings by size
Postage is set by the USPS, not by your printer, and it is driven mostly by size class. The three tiers you will run into are:
- Postcard price: the lowest First-Class tier, for rectangular cards inside the 4.25 by 6 inch maximum.
- Letter price: for cards larger than the postcard maximum, up to 6.125 by 11.5 inches and 0.25 inch thick.
- Flat price: for pieces larger than the letter maximum.
The takeaway: staying at or under 4.25 by 6 inches keeps you on the cheapest tier per piece, which adds up fast across a few thousand cards. Rates change periodically, so confirm the current price with the USPS before you budget, and remember that presorted automation mailings usually beat single-stamp retail postage per piece.
Printing cost is separate and depends on stock, quantity, and finish. You can see live per-unit pricing on every postcard page, and the specs panel further down pulls real numbers for direct mail postcards straight from the configurator.
Paper, thickness, and aspect ratio rules
The USPS cares about how a card behaves in a sorting machine, and stock is a big part of that. A postcard needs enough rigidity to feed without jamming, which is why the thickness floor is 0.007 inches. Flimsy paper bends and bunches. Overly thick board will not machine at the postcard price.
There is also an aspect ratio rule for machinable mail. The length divided by the height should fall between 1.3 and 2.5. A 6 by 4 inch card is 1.5, safely inside the range, while a nearly square card can fall outside it and pay a nonmachinable surcharge. When in doubt, stick close to the classic postcard proportions.
Most 4OVER4.COM postcard stocks are chosen to satisfy both rules by default, so a standard order feeds cleanly. If you want a premium feel, compare finishes across postcards printing and check that any specialty stock still lands in the mailable thickness range before you order a full run.
Setting up a mail-ready postcard file
A compliant size means nothing if the file is set up wrong. Here is the short checklist that keeps a postcard both print-ready and mail-ready.
- Add full bleed. Extend background art 0.125 inches past every trim edge so no white slivers appear after cutting.
- Respect the safe margin. Keep text and logos at least 0.125 inches inside the trim so nothing important is cut off.
- Use 300 DPI art. Low-resolution images look soft in print and can blur an address line.
- Keep the clear zones empty. No art or text in the barcode corner or over the address block.
- Build in CMYK. Design in the print color space so what you approve is what prints.
If you would rather not wrangle a template, the online designer sets bleed, margins, and the address layout for you. Prefer to check your own art first? Our free proofs let you confirm the file before the press runs.
Bulk mail, EDDM, and direct mail options
Once you are mailing in volume, two paths open up that lower cost per piece.
Presorted direct mail. When you mail enough pieces and presort them by ZIP, you qualify for automation rates below single-stamp postage. This is the standard route for list-based campaigns, and it is exactly what direct mail postcards are built for.
Every Door Direct Mail (EDDM). EDDM lets you blanket a postal route without buying a mailing list, but it uses larger, flat-size pieces rather than standard postcards, so plan the size accordingly. It suits local businesses saturating a neighborhood.
Not sure which fits? Our direct mail services print, address, and drop the mailing for you, and the direct mail formats article breaks down which layouts pull the strongest response.
Common postcard mailing mistakes to avoid
Even careful designers trip on the same handful of issues. Avoid these and your drop goes smoothly.
Designing into the barcode corner. The single most common rejection. Keep the lower right of the address side clear.
Going one size too big by accident. A card at 4.5 by 6.5 inches feels like a postcard but prices as a letter. Confirm your trim size before ordering.
Reverse-type addresses. White text on a dark background reads poorly on scanners. Keep the delivery address dark on light.
Picking a stock that will not machine. Too thin bends, too thick jams. Stay in the 0.007 to 0.016 inch window for the postcard price.
Skipping the proof. A quick proof catches a mislaid address block before you commit a full run. When the layout is right, order with confidence from 4OVER4.COM postcards printing.
Specs and pricing
Direct mail postcard specs and pricing
When your layout is mail-ready, here is what a made-to-order direct mail postcard gives you at 4OVER4.COM, with live specs and price-per-unit straight from the configurator.
| Quantity | Price Per Unit | Total |
|---|---|---|
| 500 | 17.9¢ | $89.68 |
| 1,000 | 17.1¢ | $170.53 |
| 2,000 | 9.35¢ | $186.95 |
| 3,000 | 6.84¢ | $205.13 |
| 4,000 | 5.58¢ | $223.31 |
| 5,000 | 4.83¢ | $241.51 |
| 6,000 | 4.56¢ | $273.85 |
| 7,000 | 4.37¢ | $306.18 |
Print it
Order mail-ready postcards at 4OVER4
Wally explains postcard rules
Right size, clear corner, lowest postage
Wally treats a postcard like a ticket the mail machine has to read: keep it inside the size window, leave the barcode corner clear, and put the address on the right, and it sails through at the cheapest postcard rate. Drift one size too big and it quietly prices as a letter. Start with a mail-ready card built to spec at 4OVER4 and the post office does the rest.
Order direct mail postcards →See it in use
Real postcard work, printed in-house
Explore more
Where to go next
By the numbers
Printing you can count on at 4OVER4
Common Questions
Common questions about USPS postcard guidelines
What are the USPS postcard size requirements?
To mail at the USPS postcard price, a card must be rectangular and fall between 3.5 inches high by 5 inches long (minimum) and 4.25 inches high by 6 inches long (maximum), with a thickness from 0.007 to 0.016 inches. A card larger than the maximum is still mailable, but it prices as a First-Class letter instead of a postcard. Standard postcards from 4OVER4.COM are built to hit that window out of the box.
What are postcard clear zones?
Clear zones are areas the USPS asks you to keep free of graphics and text so its equipment can read the piece. The most important one is the barcode clear zone in the lower right corner of the address side, roughly 4.75 inches wide by 0.625 inches tall. Postal machines print or scan a routing barcode there, so any design that runs into that corner can slow or reject the mailing.
What are the USPS postcard guidelines in plain terms?
They come down to four things: stay inside the postcard size window, keep the address side laid out correctly with the address block on the right, leave the barcode clear zone empty, and use a stock thickness the machines can handle. Get those right and your card qualifies for the lowest postcard postage tier and moves through automation without surcharges.
How do I choose the right postcard for my mailing?
Start with your goal and budget. A 4 by 6 inch card keeps you at the postcard price and works for reminders and offers. An oversized card commands more attention but mails at letter rates. Direct mail postcards are built for list mailings, while die-cut and specialty stocks help a card stand out. Compare live specs on any postcard product page at 4OVER4.COM before you commit.
What does a postcard cost and how is postage set?
Two costs are in play: printing and postage. Printing depends on size, stock, quantity, and finish, and you can see live per-unit pricing on each product page. Postage is set by the USPS and depends on size class (postcard versus letter versus flat) and whether you mail at retail or presorted automation rates. Bulk direct mail through presort typically lowers the per-piece postage compared with single stamps.
Where does the address block go on a postcard?
On the address side, keep the right half for mailing. Postage or the indicia goes in the top right corner, the return address goes in the top left, and the recipient address prints parallel to the longest edge in the lower right region, above the barcode clear zone. The left portion of that side, or the entire reverse, is yours for the message and artwork.
Can I mail an oversized postcard?
Yes. A card larger than 4.25 by 6 inches still mails, it simply moves up to First-Class letter pricing (up to 6.125 by 11.5 inches and 0.25 inch thick) or to flat pricing beyond that. Oversized postcards get noticed in the mailbox, so many businesses accept the higher postage for the extra impact. 4OVER4.COM prints both standard and oversized sizes.
Get Started
Ready to print a mail-ready postcard?
Pick your size, drop in your design, and we print a USPS-compliant postcard that qualifies for the lowest postage tier.
Legal Disclaimer
Gold Standard guarantees apply to all standard orders placed through 4over4.com. Price match requires verifiable proof of a competitor's published price for an equivalent product with matching specifications and turnaround time. Satisfaction guarantee covers manufacturing defects and print quality issues. Contact support with order number and documentation. On-time delivery rate based on tracked orders 1999 to 2026. Individual results may vary based on shipping carrier performance.
