Question: how many stamps do i need to mail a letter to puerto rico?
Answer: Puerto Rico is, like Alaska and Hawaii, a U.S. territory. You pay the domestic rate to send any mail there. Assuming you are in the US it's the same as you would need to mail a card to your nextdoor neighbor. Puerto Rico is a U S possession so one 55 cent stamp, for a letter that weights 1 ounce or less.