I think most people don't worry too much about the calories of the food and instead go by weight. Anywhere from 1 to 2lbs food per day should suffice. Usually you carry a variety so the pounds of food will be roughly equal in calories no matter what you put in there. Within reason, of course.
When I hiked the PCT my strategy was to eat as much as I possibly could and then eat even more when I got to town. I never weighed the food I brought with me, and I rarely ate all of it even though I was hungry. I guess I probably ate about 1.5 pounds per day, sometimes less.
Now that I'm just an ordinary hiker, I take about a pound a day. I try to go for very nutritionally dense foods that might be slightly heavier: lots of fat, dates, cheeses, dehydrated sweet potatoes, dehydrated meats. No pasta, oatmeal, sugar or refined packaged foods.