It takes 216 12-inch by 12-inch tiles to tile a room of 216 square feet. This is easily determined by finding the area of the tile, which is 1 square foot in this case, and dividing it by the area of the room.
One can also determine how many tiles are needed by finding the area of the tile in square inches and the area of the room in square inches. The area of the room is then divided by the area of the tile. There are also many online calculators that calculate how many tiles are needed in a given situation.