18..
144
A 19' x 15' room is 285 square feet or 26.477 square meters.
18 x 18 inch square is equal to 3/2 x 3/2 foot square = 9/4 square foot. To cover 154 foot square (you don't mean 154 square feet) is (154 x 154) / (9/4) = (154 x 154 x 4) / 9 = 10540.44, so you will need 10541 tiles
One, if it is big enough.
144
1
18..
144
6
A 19' x 15' room is 285 square feet or 26.477 square meters.
18 x 18 inch square is equal to 3/2 x 3/2 foot square = 9/4 square foot. To cover 154 foot square (you don't mean 154 square feet) is (154 x 154) / (9/4) = (154 x 154 x 4) / 9 = 10540.44, so you will need 10541 tiles
240 square tiles are needed
One, if it is big enough.
640
195 12 inches x 12 inches is 1 square foot
A square foot will cover a square foot, regardless of the depth of the material the cover is made of.