Air Miles Calculator and USA Today are two websites that help you calculate the air distance between two cities. However, an airline carriers' official website may use a slightly different calculation.
Air Miles Calculator lets you find the distance between up to four different airports and displays a map of the selected route. The USA Today website calculates base air miles and includes advanced features for determining the number of frequent flier miles you can earn for any given trip. USA Today's formula lets you tag on bonuses for elite flier status, class of service, special promotions or minimum miles earned per segment.