A hole is classified by its par, the number of strokes a skilled golfer should require to complete play of the hole. For example, a skilled golfer expects to reach the green on a par-four hole in two strokes (This would be considered a Green in Regulation or GIR): one from the tee (the "drive") and another, second, stroke to the green (the "approach"); and then roll the ball into the hole in two putts for par. Traditionally, a golf hole is either a par-three, -four or -five.
Primarily, but not exclusively, the par of a hole is determined by the tee-to-green distance. A typical length for a par-three hole ranges between 91 and 224 meters (100 - 250 yd), for a par-four hole, between 225 and 434 meters (251 - 475 yd). Typically, par-five holes are at between 435 and 630 meters (476 - 690 yd). These distances are not absolute rules; for example, it is possible that a 450 meter (492 yd) hole could be classed as a par-four hole, since the par for a hole is determined by its 'effective playing length'. If the tee-to-green distance on a hole is predominantly downhill, it will play shorter than its physical length and may be given a lower par rating. Par ratings are also affected by factors affecting difficulty; the placement of hazards or the shape of the hole for example can sometimes affect the play of a hole such that it requires an extra stroke to avoid playing into the hazard or out-of-bounds.
Eighteen hole courses may have four par-three, ten par-four, and four par-five holes, though other combinations exist and are not less worthy than courses of par 72. Many major championships are contested on courses playing to a par of 70, 71, or 72. In some countries, courses are classified, in addition to the course's par, with a course classification describing the play difficulty of a course and may be used to calculate a golfer's playing handicap for that given course.