OPENING WIDTH: a little wider then the widest part of your pet.
OPENING HEIGHT: measure from the top of the shoulders to the chest just behind the front legs.
We recommend the “Cardboard Test” to ensure correct size for your pet. Using the OPENING SIZE measurement in the charts, cut a hole in a piece of cardboard, and see if your pet can pass through easily. Or wedge open a house door the OPENING WIDTH, and block off the OPENING HEIGHT (starting just above your pet’s shoulder) and call your pet through. Pets duck their heads as they push open their door and step through it, so ideally you should install the pet door with the top of the opening just above your pet’s shoulder. But any position will do as long as your pet can open the door and get through comfortably.