Use
www.gcmap.com to calculate the distance
then use this table
Flight distance are for each segment in your itinerary and
not for the itinerary. Example, for DTW-ORD-LAS award, which comes to 235+1514 miles for a total of 1749 miles will be charged 4,500+10,000 miles for a total of 14,500 miles one-way and
not 10,000 for the total distance traveled.