1st you need to look up the carrier and route.
Then go on http://www.gcmap.com/ , enter the route, look up the total miles, then go on wheretocredit.com, enter the booking class of the ticket (you can find that by either using ita matrix or by purchasing tickets from expedia.com, on the itinerary details page it shows the ticket class) and voila, you'll see how many miles you'll get for your trip.