Course and slope ratings are calculated by the United States Golf Association. In fact, the USGA trademarks and licenses its USGA Course Rating and USGA Course Slope Rating to the Royal Canadian Golf Association -- countries other than America and Canada are unlikely to have Slope Ratings. A Course Rating measures the difficulty of a golf course and is a crucial component in determining a player's handicap. The Slope Rating measures the difficulty of a golf course for a bogey golfer. The Course Rating and the Slope Rating typically are printed on the scorecard for a golf course.
Adopt the scratch golf standard. To determine the Course Rating for a particular golf course, the USGA determines what score a typical scratch golfer -- a golfer who shoots even par under normal conditions -- would shoot on the course. A typical scratch golfer, as defined by the USGA, hits 250-yard drives and can reach a 470-yard hole in two strokes. A typical female scratch golfer hits drives 210 yards and can reach a 400-yard hole in two strokes.
Apply the Course Rating process. The rating process is done by a team of people who consider many factors in determining what a scratch golfer would typically shoot on each hole. In addition to the raw length of the hole, the USGA team considers other factors that might affect the "true" playing length of a hole, including the amount of roll, elevation, doglegs or forced lay-ups, prevailing wind direction and altitude. The team also considers a number of potential obstacles, such as sidehill lies, width of fairways, difficulty of hitting the green, difficulty of the rough, bunkers, out-of-bounds areas, water hazards, green speed and the number of obstacles close to a landing area, which the USGA labels the "psychological" factor.
Add or subtract the evaluation number from the par for the course. The Course Rating is a number with a single decimal. For example, if an extremely difficult par-72 golf course is a plus 3.0, the Course Rating would be 75.0. If an easy par-70 layout was rated a minus 2.0, the Course Rating would be 68.0. A typical scratch golfer should therefore shoot 75 on the difficult course and 68 on the easy course under good playing conditions.
Calculate the typical score a bogey golfer would shoot on a golf course in good conditions to determine the Slope Rating. The USGA does this by evaluating in detail what a typical bogey-per-hole golfer would shoot. Statistics have determined that the difficulty of a course will impact bogey golfers more than scratch golfers, and the Slope Rating is a measure of this difference. It is expressed by a number from 55 to 155, with 113 being the average Slope Rating. A course that poses difficulty and leads to higher scores by bogey golfers will have a higher Slope Rating than a course that is less challenging. The USGA calculates Slope Rating with the following formula: bogey course rating minus Course Rating, with the result multiplied by 5.381 for men or 4.24 for women.