PetSafe Pet Screen Door - Dog and Cat Door for Screen Door, Window and Porch Use EASY TO INSTALL: Small size door snaps directly onto existing screens in your home for quick and easy outdoor access for your dog or cat STORM DOOR, WINDOW, AND PORCH COMPATIBLE: Works with most metal or vinyl coated fiber screen storm doors, window screens or screened-in porches DURABLE SCREEN MESH MATERIAL: Specially designed mesh material is safe and durable for pet use; puncture and tear-resistant SAFE AND SECURE: Small size door has durable high-impact frame with dual sliding locks, allowing you to restrict outdoor access whenever you want SIZE INFORMATION: For pets under 30 lb.; flap opening size is 8 in. W x 9 1/4 in. H; measure your pet to ensure comfortable use HERE TO HELP: Call, email or chat with our expert U.S.-based Customer Care specialists six days a week; they are ready to assist you and your pet EXPERIENCE: PetSafe brand is an industry leading U.S. manufacturer of pet behavior, containment and lifestyle products since 1991, helping millions of people and pets each year <span class="a-text-bold">Measure Width: </span>Measure the widest part of your pet&#039;s body - either the chest or the hips. Add 2 in. to this measurement. <span class="a-text-bold">Measure Height: </span>Measure your pet from the top of the shoulders to the bottom of the chest or  belly - whichever length is greater.  Add 2 in. to this measurement. <span class="a-text-bold">Compare Measurements: </span>Check the chart below.  If the pet&#039;s width and height measurements (+ 2 in.) are less than those of the door, you&#039;re all set.