Well a good sized shoebox is 16 x 10 x 6 inches so that would be a total of 960 cubic inches. If a card box is 3.6 x 2.6 .75 inches (total of 7.1175) cubic inches. That would mean 960 cubic inches fits 134.87881 decks. Therefore, 134.87881 decks multiplied by 54 cards per box is ~7,283 cards total.
So I say 7,283 cards in the box.