How many 18x18 square inch tiles are needed for 670 square feet?

Answer 1

Area of each tile = 18in x 18 in = 1.5 ft * 1.5 ft = 2.25 sq ft.

Number of tiles required = 670/2.25 = 297.77... tiles, that is a minimum of 298 tiles.

That is the mathematical answer. It assumes that the shape to be covered is "well-behaved", that almost all offcuts are used and that there is almost no wastage. In real life all three assumptions are unrealistic and you should make an allowance of 5-7% - more if you are not an expert.