18 x 28 = 504. 504 / 144 = 3.5
You will need a minimum of 136 18" x 18" tiles but buy a few extra to account for breakage, etc.
2.78 square feet.
2.77 square feet.
2.25 square feet.
3.5555 square feet.
1.7689
40 square feet.
Approximately 179.17 square feet.
Approximately 222.54 square feet.
Approximately 122.28 square feet.
There are 144 18 square inch tiles in an area of 18 square feet.
90 square feet