What Size Is A Postcard

The Actual Dimensions That Matter for Mailing

The USPS standard postcard size is 4 inches by 6 inches. This is the minimum size you can send for the current postcard rate without paying letter postage. Anything smaller than 3.5 by 5 inches gets classified as a small square envelope and the pricing and processing rules shift entirely. If you are designing for print and mail, sticking to 4x6 means your piece runs through automated sorting machinery without getting flagged or requiring manual handling fees. The standard A6 size used internationally is 105 by 148 millimeters, which comes out to roughly 4.13 by 5.83 inches. It is essentially the same footprint as the US standard with a tiny bit of breathing room on each edge. This is the size you see most often on European mail and it works fine in the US postal system, though the slight difference from 4x6 can confuse designers who export templates expecting exact alignment with pre-printed envelopes or mailing trays.

What Size Is A Postcard for Domestic vs International Mail

For domestic USPS mail, a postcard must fall between 3.5 by 5 inches and 6 by 4.25 inches to qualify for the flat rate, provided it meets thickness and rigidity requirements. The thickness has to be no more than 0.016 inches and no less than 0.007 inches. This is where things get tricky and most people mess it up. I once designed a batch of 4x6 postcards on 16-point cardstock for a client who wanted them to feel substantial. The cards measured about 0.02 inches thick after cutting. Every single one got routed to manual processing at the sorting facility, which added handling time and cost. The workaround was switching to 14-point matte cardstock, which brought the thickness down to roughly 0.014 inches and kept them in the automated line. You can test your stock thickness with a micrometer before committing to a full print run, or just ask your print shop for the caliper measurement on their stock options. International postcards follow different rules set by the Universal Postal Union. The standard maximum is 240 by 105 millimeters and the minimum is 140 by 90 millimeters. If you send a 4x6 card to Canada or Europe, it fits within those bounds, but the postage rate jumps significantly. The current international postcard rate from the USPS is substantially higher than the domestic rate, and some countries impose additional surcharges for non-standard sizes or heavy cardstock.

Designing Around the Actual Constraints

The print industry standard for a 4x6 postcard includes a 0.125 inch bleed on all sides, meaning your final artwork should be 4.25 by 6.25 inches with design elements extending to the edge. When the sheet gets trimmed down to 4x6, anything within that 0.125 border is the safety zone where critical text and graphics need to sit. If you place important content right at the trim line, a half-millimeter shift during cutting can clip it off. I have seen this happen repeatedly with client files where the address block or a QR code sat at the very edge and came out partially cut on half the run. Gsm and pt ratings are not interchangeable. This is one of those things that confuses people who design on their own. In the US, cardstock is commonly measured in points, where one point equals roughly 0.001 inches of thickness. In Europe and many parts of the world, gsm measures weight per square meter. A 14pt card is approximately 300gsm, but the conversion is not exact across all brands and finishes. Coated stocks are denser and thinner for the same weight compared to uncoated. This matters when you are trying to hit that 0.016 inch threshold for postcard-rate postage. If you are sending a large quantity, the paper finish affects postage eligibility too. A heavily textured or embossed postcard can exceed the thickness limit even if the base stock is within spec. I learned this the hard way with a client who wanted a spot UV gloss on a custom logo. The UV layer added enough buildup at certain points that the cards barely made the rigidity cutoff. We ended up pulling the UV treatment and going with a standard matte finish, which kept the thickness down and preserved the postcard rate. For small batches, you can order a physical proof from your printer and run it through a caliper or even just flex it against a known-good postcard to get a sense of whether it will sort correctly.

Square postcards at 6 by 6 inches do not qualify as standard postcards under USPS rules. They exceed the 6 by 4.25 inch maximum dimension and get reclassified as a small flat, which costs significantly more to mail. This is a common mistake for designers who think bigger is better and then wonder why their mail cost triple. The 4x6 size is the sweet spot for a reason. It uses standard envelope windows, fits mailing trays, qualifies for the lowest rate, and people can easily read both sides while holding it. For budget-conscious projects, digital printing on 14pt white cardstock at 4x6 with a quarter inch bleed is the most reliable route. It keeps postage predictable, turnaround is usually two to five business days for a standard run, and the cost per unit drops fast once you move past a few hundred copies. Offset printing makes sense only when you are running thousands of units, because the plate setup cost is not recovered until volume is high enough to spread it out.