How many 9x9 tiles will I need for 100 square feet?

Answer 1

Assuming the 9" x 9" tiles have patterns with obvious edges (so you only want to join them edge-to-edge), and assuming the 100 square feet is in fact a square (10' x 10', or 120" x 120"), then you'll need 183 tiles to cover it.

You'll make a square starting in one corner, 13 rows of 13 whole tiles each. That's 169 tiles (and 13 x 9" = 117"). That will leave a 3" wide strip along the two edges and opposite corner of your square. Take 13 more tiles and cut them into thirds (as 3" strips), discarding the middles. Use half of those ⅓-width tiles along one edge of your square, and the other half along the other edge. That's 182 tiles — and then you cut a 3" x 3" square off your last tile, to finish the corner of your area.

Note: If you don't care about joining the tiles only at their edges, then you only need 178 tiles.