The Crain 18″ Vinyl Tile Cutter,CLICK HERE will have no problem cutting tiles straight or 12 inch tiles diagonally. It has a steel reinforced blade carrier and large, rigid base to ensure straight, accurate cutting. It comes with a straight cutting guide, diagonal cutting guide, and a self-measuring floor guide for repeat cuts. Position the floor guide against the edge of the last field tile, then slide the tile to be cut underneath the blade and all the way against the wall. When the tile is cut, the width that is cut off automatically equals the amount needed to cover the remaining subfloor. This cutter also has built-in low-profile blade height adjustment knobs that provide fast and easy adjustment.