Postcard Dimensions That Actually Work for Mailing

The USPS considers anything under 6 inches by 12 inches and over 3.5 inches by 5 inches to be a standard postcard. The most common size you will see around is 4.25 by 5.5 inches. This is called A2. It fits a standard #10 envelope if you fold it, which makes stuffing bulk mailboxes at least somewhat tolerable. Most people designing their first batch of postcards pick a size based on what looks nice in their head. That tends to go poorly. Printers have minimum margin requirements, and the postal service has rigid dimensional rules that determine whether your piece qualifies as a letter or a flat. Cross those thresholds and your postage doubles overnight.

The Typical Postcard Size Understanding The Standard Dimensions For Maximum Impact

If you want to avoid surprises, start with one of these established sizes and build outward from there:

A2: 4.25 x 5.5 inches. This is the workhorse. Fits standard envelopes. Works for everything from wedding save-the-dates to direct mail flyers. First-class postage at the time of writing is still in the single-digit cent range for this size when mailed as a postcard. A6: 4.25 x 6 inches. Slightly taller. Feels more substantial without triggering flat rates. A lot of photographers prefer this because it gives more vertical space for portrait-oriented images. 5 x 7 inches. The classic greeting card size. Heavier stock feels appropriate here. You will pay more in postage but you also get more real estate for a full bleed design.

6 x 4 inches. Wallet-sized horizontal. Common for photo postcards sent from tourist destinations. Cheap to produce in bulk but easy to overlook in a mailbox full of larger cards.

Here is the thing nobody tells you until they have already paid for it: the printable area is never the full dimensions of the card. Every professional printer requires a bleed of about 0.125 inches on each side and a safety margin inside that bleed. If you are sending designs to print, your critical text and important visual elements need to sit at least 0.25 inches away from every edge. Otherwise a guillotine trim that is off by a fraction of an inch will chew into your words. I ran into this once with a local brewery that wanted their logo flush against the edge on a 4.25 by 5.5 card. The printer trimmed the batch and three hundred cards had half their logo missing. The fix was simple enough - I redesigned the layout with a 0.25 inch internal margin and asked them to re-output. We caught it before the run. They ate the cost of the proof but learned not to argue with the margin rule again. Going beyond standard dimensions is possible but it stops being economical very quickly. Once your card exceeds 6.125 by 11.5 inches or goes over 0.009 inches in thickness, the USPS reclassifies it as a flat. Postage jumps from roughly 0.73 cents to over 1.50 per piece depending on weight. That is a hundred percent increase for a marginally larger format. Another thing that catches people off guard is the weight-to-postage relationship. A 100lb dull coated card at A2 size with one side printed weighs about 0.9 ounces. That stays in the postcard rate band. Add a second side print and you might push into the next weight tier, which triggers letter rates instead. I always ask clients to run a dimensional weight calculation before they finalize their design. It takes twenty seconds on any postage calculator and saves a real amount of money on a 10,000-piece run. Paper choice also matters more than most beginners realize. A 16pt cardstock will feel premium but it is harder to fold cleanly if you need a fold line. A 14pt is easier on the binding equipment and cheaper per unit. The difference in feel is almost imperceptible to most recipients unless they are holding both side by side.

Designing Within the Constraints

Set your document up at the final trimmed size, not the stock size. Add your 0.125 inch bleed on all four sides. Keep all text and logos inside the 0.25 inch safety zone. Use CMYK color mode, not RGB, because your printer is mixing inks, not light. Include crop marks if your designer is handling the file, though most modern print shops will do this for you automatically. For bleeded designs, extend your background color or image all the way to the edge of the bleed area. Do not stop the color at the trim line and expect it to look right. You will get a thin white border around the entire card, which looks amateurish and wastes the space you paid for. If you need a free template to start from, search for "postcard template 4.25x5.5 cmky bleed" and you should find several reliable options from printer websites. Marq, Canva, and Adobe Express all have premade layouts sized correctly. The downside is that premade templates sometimes include their own margin rules, so check the safe zone before you drop your content in.

When Standard Sizes Fail You

There are cases where a non-standard size makes sense. Square postcards at 5 by 5 inches stand out in a mailbox full of rectangles. The tradeoff is that they do not fit standard envelopes and some automated sorting equipment at the post office handles them less gracefully. You also pay more per unit because square blanks waste more material during cutting. Thin and wide formats around 3.5 by 8.5 inches exist as a middle ground but they sit awkwardly between postcard and letter classifications. Some printers treat them as mini-postcards. Others push them into the letter rate. Call your printer and ask how they classify it before you commit. The honest limitation here is that no matter how well you design, the physical act of getting the card through the mail system introduces variables you cannot control. Paper warps in humidity. Cards get bent in sorting machines. A 10,000-piece run will always have a small percentage arrive damaged. Budget for a 2 to 5 percent spoilage rate and order accordingly rather than assuming you will get exactly what you paid for.