Actually it depends on whether it's a long course or short course meaning the answer could be anywhere from 4.8 to 5.2.
Seriously, according to Wiki:
The length of each hole from the tee placement to the pin determines par values for each hole primarily, though not exclusively. Traditionally, holes are assigned par values between three and five strokes. For a casual player from the middle tees, an average par-three hole will range between 100 yards (90 m) to 250 yards (230 m) from the tee to the pin. Average par-four holes range between 250 yards (230 m) and 450 yards (410 m), although tournament players will often encounter par-four holes as long as 500 yards (460 m) or more as it is not uncommon for short par-five holes for normal play turned into par-four holes in championship play. Average par-five holes are between 450 yards (410 m) and 600 yards (550 m), but in the 21st century holes of over 600 yards (550 m) are becoming more common in championship play. Other considered factors include terrain and objects that may require a golfer to take fewer or more shots to overcome (such as trees, water, hills, or buildings).