Homeowner

16^2 is 256. divide 800 by 256 to get 3.125. Therefore, you need 3.125 16x16 tiles, but if you need a whole number then you need 4 16x16 tiles.

800 square feet is   800 x 12 x 12 = 115200 square inches

Each tile is 16 x 16 = 256 square inches

115200/256 = 450 tiles