How many interviews is best?

This is going to vary from job to job, and candidate to candidate. But, a good rule of thumb when you get to the Decision Round, is to divide the candidate's past experiences up into manageable chunks where each interviewer covers 1-2 jobs from the candidate's past in their interview. 

For candidates with a long career history, you may want to focus your interviews only on the most recent, relevant experiences, with a light touch on older, less relevant roles. 

Similarly, for entry level roles and candidates with minimal job experience, you may want to consider focusing some of the interview time on their experiences in high school, university or grad school - we've provided some interview templates that will help to guide you through those interviews also.