If you mean 12x12 "inches", then each tile covers 1 square foot. We trust you can take it from there.
12x12 is 144 and 11x11 is 122
If 12x12 is 144... There would be 144 tiles in a box right?
If you're talking floor tiles as opposed to wall tiles and by 12x12 you mean they are 12 inches square, then the answer is 300. Because each tile is one square foot and a 15'x20' room is 300 square feet. Simple, eh?
A gross is a dozen dozens (12X12) why it is called a gross i couldn't find out.
12X12 12X12
12x12= = 144
144
72
Since a 12x12 tile is one square foot, then 38 12x12 tiles will cover 38 square feet.
80 if the tiles are 12x12 - 12x12 is one square foot covering 80 you would need 80 tiles
12x12