What size PlexiDor do I need for my Chihuahua? An average size Chihuahua will need a small PlexiDor. The average size Chihuahua weighs between 3 and 6 pounds. The small PlexiDor is constructed for dogs up to 9 pounds and cats up to 24 pounds. The weight difference is due to the difference in build between dogs and cats. The opening size is 6 1/2″ x 7 1/4″ and the door is usually mounted 2″-4″ above the floor. The top of the opening should be just above the dog’s back. Other common breeds that use the small door include Pomeranians, Papillons, Yorkies, and Maltese. The below size chart shows installation cut hole, opening for pet, and overall size, click on it to get the full size version.