If you need a Replacement Flap for your Pet Door, you have come to the right place. Before ordering a Pet Door Replacement Flap, make sure your current pet door flap is the same measurements as those shown in the tables below. Also, we offer two types of Pet Door Flaps, The Dual Pet Door Flap and the Single Pet Door Flap. Dual Pet Door Flaps have a main flap area and a "U" shaped outer flap. The Single Pet Door flap is all one piece. Please make sure you are ordering the correct Pet Door Flap the Classic PetSafe Pet Door will use a single flap and the Ultimate Pet Door will use a douuble flap. Measurements include the complete pet door flap including the area where the pet door flap attaches to the pet door frame. Your pet door opening may be slightly smaller that's OK we have also oganized the by pet door.