What size greeting cards require extra postage?

Postage surcharges come down to shape, size, and thickness, not just weight. A few common greeting card formats trigger extra USPS charges, so it pays to check before you commit to a design.

• Square cards always require the USPS non-machinable surcharge, no matter how small.
• Envelopes larger than 6.125" x 11.5" need extra postage.
• Anything thicker than 0.25" is also surcharged.

Standard rectangular cards like 5" x 7" in matching envelopes mail at regular first-class rates. If you love a square design, just budget for the surcharge up front.