Companies sometimes stipulate an interviewing period so you may have to wait until that time is up. If you impressed them they would have told you there and then or called you a couple of hours after.
Keep your chin up and let everyone know how you got on. Who was the company and what was the position?
They probably had a number of applicants who they will interview over a few days so you will have to wait until all potential employees have been seen. In future you could always ask, at the interview, when you would be notified of the outcome. If you don’t hear from them give them a call and discuss why they didn’t select you. This will give you areas to focus on in any future applications.
Good Luck
IOMAndy: try this, it took me seconds to find 🙄