A 10 x 10-foot room requires 100 square feet of tile plus a 10 percent amount for waste and cuts, or 15 percent if the room is oddly shaped. It is best to estimate slightly more than the job requires so as to not run short.
When determining the amount of tile necessary, take into account the room shape in addition to the shape of the tile to be used. A regular square or rectangular room needs less tile than an oddly shaped room. Most tile comes in boxes with the amount of square footage it covers in a typical installation.