What are the standard postcard dimensions and the costs to mail?

The standard dimensions for postcards that can be mailed at the First Class rate of $0.29 are as follows:

Any items smaller than 3 ½” are not mailable. For postcards, length is the dimension parallel to the address. Postcards must be rectangular and be made of unfolded and uncreased paper or card stock. Large cards that exceed the maximum dimensions of a postcard pay the First-Class Mail letter, large envelope price of $0.44.