According to The Boxer Dog Site, if your dog weighs 10 to 25 pounds, feed him 1 1/2 to 2 cups a day.
If he's between 25 and 50 pounds, give him between 2 and 4 cups a day.
A boxer weighing between 50 and 75 pounds needs 4 to 5 cups a day.
Larger boxers weighing 75 to 100 pounds require 5 to 6 cups daily.