|But to qualify for mailing at the First-Class Mail postcard price, it must be:. Mail
Entry Unit staff, who can tell you if your mailpiece design will be mailable.Postcard Sizes Small Postcard Postage Rates Jumbo Postcard Postage. Jumbo
Postcards - postcards that are larger than 4¼″ x 6″ cannot be mailed at the . Standard Postcard Size Information for Printing, Design & Mailing. Q: What are
the postcard sizes that can be mailed in bulk and those that comply with the . May 14, 2014 . Postcard size is 3.5 x 5 to 4.25 x 6, anything larger is considered to be in thick,
anything less is not mailable unless you put it in an envelope.All measurements are in inches. These are standard postcard sizes. Check with
United States Post Office before mailing. Designers Toolbox is not responsible . The USPS also requires the postcard be between 0.007 inch and 0.016 inch thick
. Postcards under the minimum size or weight are not mailable. Above the .