How many 18 x 18 inch tiles are needed for 195 square feet?

Answer 1

18" x 18" = 1.5' x 1.5' = 2.25 sq ft.

So the number of tiles needed = total area/area of each tile = 195/2.25 = 86.66.. that is, a minimum of 87 tiles.

That is the mathematically correct answer. In real life, though, you need to allow for breakages and wastage. This allowance will depend on your skill level and the shape of the 195 sq ft area. Some areas will require a lot more tiles to be cut or trimmed than others and all that could add to the wastage.