It only takes a single stamp. But it does have to be the correct denomination. Currently the rate for one ounce from the US to Ireland is 98 cents for a postcard or the first ounce of mail.
1
Lots.
1 stamp is required.
sometimes 2 if its big if letter then one
Ask at a post office in Oregon.
Just one of the correct denomination for the fee or any combination of stamps of smaller value to make up the fee.
3 stamps!
700 Stamps
how many forever stamps = .94
I successfully mail CDs all the time with 2 stamps.
4 stamps
If this is just a post card you will only need the one stamp to mail it within the US.