Originally Posted by
IAHtraveler
The other (cheating) trick is to use milecalc.com. You can put in your routing (only up to 4 segments, though) and it'll give you the total miles. On the second page, you can put in specifics (cost, airline program & % bonus, booking class bonus, promo miles, credit card miles, etc) and it will give you the exact cost/mile for both the 1-way our round trip option.
For a 10 second search, I found PVD-ORD-SEA for 2570 miles instead of your 2560 and it shows 8.17 cpm without any bonus mileage selected.
If you click the more complex routings option milecalc allows as many segments as you like, it also caters for open-jaws.