How many stamps to send letter to APO AE 09378 from US?

To send a letter to APO AE 09378 from the U.S., you typically need one First-Class Forever stamp, which covers the cost of mailing a standard letter (up to 1 ounce) domestically. If your letter exceeds 1 ounce, you will need additional postage. It's always a good idea to check with your local post office for the most current rates and requirements, as they can change.