What size PlexiDor do I need for my Beagle? An average size Beagle will need a medium PlexiDor. The average size Beagle weighs between 18 and 30 pounds. The PlexiDor Medium is constructed for dogs up to 40 pounds and a perfect fit. The opening is 9″ x 12″ and the door is usually mounted 4″-6″ off the floor. When measuring, the top of the opening should be just above the dog’s back. Other common breeds that use the medium door include Corgis, Dachshunds, Pekingese, Cocker Spaniels, and many Terriers. The below size chart shows installation cut hole, opening for pet, and overall size, click on it to get the full size version.