All measurements are in inches. These are standard postcard sizes. Check with United States Post Office before mailing. Designers Toolbox is not responsible . Standard Postcard Size Information for Printing, Design & Mailing. A: If clients cannot change the layout of their design and comply with the USPS requirements . But to qualify for mailing at the First-Class Mail postcard price, it must be:. If your mailpiece does not meet the dimensions above, then the Postal Service . Full Answer. The USPS dictates size standards for mail in the United States based on the requirements of its automatic mail-sorting equipment. The minimum . PsPrint Postcards Layout Guidelines Templates. Standard Mailing. No matter the size of your budget and your job, we have a postcard quantity option that . Standard Postcard Sizes: Postage and Requirements. See our Postcard Templates for easy postcard setup that meet all of the UP Post Office requirements for .