DOOR OPENING: The Microchip Cat Door Flap opening is 4 3/4” (H) by 5 5/8” (W) and can be installed in doors, windows or walls – accessories are available from SureFlap. MICROCHIP COMPATIBILITY: Works with 9 (Avid Secure), 10 (FDXA) and 15 (FDXB) digit microchip numbers; if unsure of your pet’s microchip number, you can check with your veterinarian, pet shelter or animal rescue.