As of June 2014, in order to send a letter from the U.S. to Peru, 3 standard stamps are required. According to the United States Postal Service, a standard size letter weighing up to 1 ounce costs $1.15 to send from the U.S. to Peru.
Three standard $.49 stamps are equivalent to $1.47 worth of postage; one that sends a letter from the U.S. to Peru using this method will overpay the postage required by $.32. Using one cent stamps in conjunction with standard stamps can alleviate this issue, but few people readily carry around this type of stamp. One can take the letter to the post office and pay the exact $1.15 that is required to send the letter. This method also ensures that the letter meets all weight, thickness and size requirements for the amount of postage paid.