The WebFlyer mileage calculator is the tool you'd want to turn to if you want to look up distances between two locations. You've got to figure out how many miles you're stockpiling away, right?
In its simplest form, distances are displayed in both miles and kilometers for both one-way and round-trip distances. Still, for someone who is looking for a little bit more of an extra info, the calculator will also go the extra mile (ha!) by calculating out the average cost-per-mile (CPM) of a flight. This is basically the metric some flyers use to calculate whether they've gotten a "deal." Most people generally say anything below 4-6 CPM is good, but this really depends on the airport you're flying out of. The lower this number is, though, the better.
The calculator also can calculate mileage bonuses, since flyers who have airline status and first- and business-class customers usually stand to earn slightly more miles. If you include an elite/class of service bonus, just realize that this gets computed into your CPM.
To get an idea for the calculator's accuracy, I recently compared the numbers against ITA Matrix. For a one-way flight, ITA estimated a LAX-YVR-IST route at 5787 miles while WebFlyer estimated the route at 5780 miles. Each estimate was definitely very close to the ballpark with only a seven-mile difference. (The airline, Air Canada, did not display the actual mileage on their website.)
It's my favorite calculator because it's simply the most fully-featured one for my purposes. And for the love of God, please don't ever use Google Maps - that calculates out land distances, not air distances. Totally two different things.
