That would ultimately depend on the weight of the letter. But for an average letter (such as a greeting card to grandma, bank statement, et cetera) you'll need a single First-Class stamp.
How many stamps are needed to send a letter from Texas to Alaska?
700 Stamps
20
one
It takes 98 cents to send a letter to Brazil from the US
If it is in the US, one stamp.
It costs $0.94 USD to send a letter to Taiwan from the United States.
-2 and 1/2
one 44c stamp
probably around 20
How much to send a first class letter to Philippines?
How much to send a first class letter to Philippines?