Depends on the type of operation and how often the aircraft is flown, and on what missions, etc. Airlines typically staff their aircraft at something like five crews (ten pilots) per airplane, but that number varies significantly.
At my company, we have one low-utilization King Air. We have two pilots, and we always fly as a crew. I know of another company that has two business jets, very high utilization (600+ hours a year on each). They have six pilots ... the idea being that four are flying, and the other two have days off, vacation, FlightSafety, whatever.
The answer to your question is "all over the map" ... there are WAY too many variables to consider.