How to Install a Dog Door

Measure the height of your dog from the floor to the lowest point of her chest or abdomen -- whichever is bigger -- and jot down the number as the "step-over height." Next, measure from the floor to your dog's shoulder, add an inch or two, and record that number as the "maximum height." Finally, measure her widest point, usually the width across the shoulders or hips. Take whichever is the largest number, add 2 inches and record it as the "minimum width."

Take the measurements to a home improvement store, and use the sizing information on the box to purchase a door recommended for your dog's size.

Remove the pins from the hinges on the door in which you will install the pet door. Use a hammer to tap the pins up from the bottom of the hinges.

Remove the door from the frame and lay it flat -- outside face up -- across saw horses. If the door is plain, indicate the bottom with a piece of tape so you do not accidentally put the pet door in the wrong place.

Find the center of the door from side to side at the bottom, and make a light pencil mark. Measure and mark a second point in the center of the door higher at approximately the height of your pet’s shoulders, and attach a length of masking tape vertically between the marks. Draw a line between the points on top of the masking tape to keep from needlessly marking your door.

Measure up the line from the bottom of the door the number of inches you recorded as the "step-over" height. Make a horizontal guideline across the door at that height. Use a carpenter’s square to ensure that the line is perpendicular to the vertical line you drew in the previous step.

Mark the center top and center bottom of the paper or cardboard template that came with your pet door kit, and place the bottom edge of the template against the horizontal guideline you drew on the door. Aligning the center points of the template with the center line on the door.

Draw the outline of the area you will cut out for the pet door, using the template as a guide.

Put a half-inch bit in your drill, and bore a hole inside each corner of the drawn pattern to serve as starting holes for the jigsaw blade.

Start the jigsaw blade in one of the drill holes, and cut out the pattern area.

Test-fit the outside portion of the dog door in the opening. Indicate the positions of screw holes on the frame by marking through them onto the door with your pencil.

Remove the frame and drill holes at the marked positions with an appropriately sized drill bit.

Assemble the dog-door frame within the opening. This may vary slightly from one door style to another, but it usually involves placing the frames within the opening, then screwing the outside frame to the inside frame through holes drilled through the main door. Follow the specific instructions in your dog-door kit.

Caulk around the frame on the outside of the dog door with a quality outdoor caulk, if desired, to waterproof the interface between the dog-door frame and main door.