This information can be found in full form at the USGA website.
Authorized golf associations issue a USGA Course Rating and Slope Rating for the most commonly played sets of tees. If a USGA Course Rating and Slope Rating from a selected set of tees are not available for the appropriate gender, the player may apply the following procedure on a temporary basis:
• Locate the nearest set of rated tees for the appropriate gender;
• Determine the yardage difference between the set of tees being played and the rated set of tees;
• Using the following table, find the range that includes the yardage difference;
Add the resulting table values to the ratings of the nearest set of tees rated for the appropriate gender if the unrated tees are longer than the rated tees, or subtract the resulting values if the unrated tees are shorter than the rated tees. This method may also be used if a player plays a combination of tees. The player first determines the total yardage played and then applies the above procedure.