There are guidelines for a holes length which determine it's par. As we all know you can have an easy par 4 or a hard par 4, but this is what course ratings are for
The USGA states "A male scratch golfer, for rating purposes, can hit tee shots an average of 250 yards and can reach a 470-yard hole in two shots at sea level. A female scratch golfer, for rating purposes, can hit tee shots an average of 210 yards and can reach a 400-yard hole in two shots at sea level.". Due to this logic of distance, the current guidelines exist...
Men:
Par 3 - Up to 250 yards
Par 4 - 251 to 470 yards
Par 5 - 471 yards to 690 yards
Par 6 - 691 yards or more
Women:
Par 3 - Up to 210 yards
Par 4 - 211 to 400 yards
Par 5 - 401 to 575 yards
Par 6 - 575 yards or more