How many 9x12 tiles need to cover 100 square feet?

Answer 1

It depends on the dimensions used for the tiles. Clearly, one tile that is 9 ft * 12 ft will cover an area of more than 100 square feet.

Second, it depends on whether or not the shape you wish to tile is "well-behaved". This will determine what proportion of the tiles will need cutting. Cutting tile will inevitably lead to wastage - unless you want a partial mosaic!