The best thing to do is to just ask at the interview when they expect a decision to be made.
This shows that you are interested in the job! Write a thank you note immediately after the interview, preferably a handwritten note.
With todays employment market it could take any where from two weeks to six weeks to hear anything back. You should send them a Thank You note for their time and call and check on the position in at least a month to let them know you are still interested.
Certainly the employer must have given an estimate of time to call you back. If that happened, wait for that time. If not, wait at least 5 business days to call them.
