You may have had some clue at the interview as to when to expect a confirmation email. If you have, then use that as a guide. If they said they would be in touch in the next few days, then I would leave five days before chasing up. If they said a week, then leave a week and a half. If they said nothing, then perhaps a week would be right. It is worth remembering that people are busy and so may just not have had the time to do it. If you do chase up then be very polite and apologetic.