It costs $1.15 to send a postcard from the United States to England through the U.S. Postal Service as of 2015. The minimum dimensions for a postcard are 5 1/2 inches by 3 1/2 inches.
Postcards that are larger than 6 inches by 4 1/4 inches but do not exceed 9 1/4 inches by 4 3/4 inches are charged at the First-Class Mail International letter price. This amount is determined by the weight of the item in ounces. This price ranges from $1.15 to $4.11. For large postcards that are nonmachinable, there is an additional surcharge of 21 cents. An item is considered nonmachinable if it has an aspect ratio (length divided by height) of less than 1.3 or greater than 2.5, has strings or other closure devices, is too rigid, or has an exterior surface not made of paper.