Specifically this is for: a card having dimensions between: 3 1/2 x 5 x .007 thick. 4 1/4 x 6 x .016 thick. To send a postcard to an international destination the rate is $1.20, up from $1.15 as of the same May `015 date. As of Jan `014 large postcards rose 3 cents to $0.49, up from $0.46 to mail. These have maximum dimensions of 11 1/2 x 6 1/8 and can measure up to 1/4 thick.