2.25 square feet
It is not clear what is meant by an "18x18 square feet" tile. 18ft * 18 ft = 324 square feet, so that one tile will be more than enough. An 18 inch by 18 inch tile cannot be a 18x18 square feet tile.
67.5
440 6-inch square tiles.
288 6-inch tiles are needed.
1.78 sq feet per tile.
A square 20-inch tile is 2.78 square feet.
3.5555 square feet.
2.25 square feet
This tile has an area of 1 ft2.
1.78 square feet.
There are 144 18 square inch tiles in an area of 18 square feet.
It is not clear what is meant by an "18x18 square feet" tile. 18ft * 18 ft = 324 square feet, so that one tile will be more than enough. An 18 inch by 18 inch tile cannot be a 18x18 square feet tile.
1.78 square feet.
67.5
Approximately 96 square feet.
2.007 sq ft