Here are some ways to know you had a perfect job interview. However I want you to remember that a perfect interview does not equate you being hired. So I don't want you to get your hopes up high. I just want you to know the signs so you don't walk out wondering.
They smiled and gave you a lot of eye contact: Eye contact is always a GOOD thing. Never underestimate it and it is a great beginning signal.
The Interviewer talked to you like you already had the job: If they start talking about the upcoming projects and advising you what needs to be done. This is a good though not confirmed sign.
The interview opened up to a personal conversation with you as if you would meet again: They start talking about their kids and the work culture in a relaxed state. thats yet another sign.
The "for sure" phrase was used at the end of the interview: If they say "we will let you know for sure by...." this is a good sign of a perfect interview. Especially if they did this before you asked to followup with them .
They gave you a tour of where exactly you would be working: The tour would be after your interview. And a really good sign is if they do it unannounced.
Salary was confirmed and discussed: They want clarity on what your requesting. that is always a great sign when combined with the other 6 signs here.
You met the CEO and or department head: Hiring mangers are NOT introducing BAD hires to their boss or the department heads.
Though none of these again guarantee you the job you can still consider yourself closer to the prize. Think good thoughts and prepare for whatever the outcome may be.