As of 2014, the United States Postal Service charges $1.15 for all international letters that weigh 1 ounce or less. For heavier letters, customers need to purchase additional postage. Prices vary based on the overall weight of the item in question.
International mail rates do not vary in the United States. Instead, First-Class postal rates are determined solely by the size and weight of the item or items. All letters must weigh less than 4 pounds in order to be considered First-Class Mail. Heavier letters and parcels need to be shipped via an alternative solution, such as Airmail or International Priority Mail.