미국에서 많이 사용되고 있는 포스트카드 표준 사이즈는 다음과 같으며, 미주바이에서 제시되지 않은 경우, 필요시 별도문의 바랍니다.
A postcard or post card is a rectangular piece of thick paper or thin cardboard intended for writing and mailing without an envelope.
Shapes other than rectangular may also be used.
There are novelty exceptions, such as wood postcards, made of thin wood, and copper postcards sold in the Copper Country of the U.S. state of Michigan, and coconut "postcards" from tropical islands.
Cards with messages had been sporadically created and posted by individuals since the beginning of postal services.
In the United States, the custom of sending through the mail, at letter rate, a picture or blank card stock that held a message, began with a card postmarked in December 1848 containing printed advertising.