I recently moved, and had to find a new home for the litter box, the bathroom. I also have two dogs, and they had taken to snacking when I wasn't paying attention. Hence, the kitty door. It needs to be big enough for the cats, but not big enough for the dogs.

Step 1: Materials Needed

Safety goggles (let's take a moment to talk about shop safety)
Tape measure
Pencil
Plate (or other 6 inchish object)
Jig saw
Square
Screwdriver
Hammer

Step 2: Measure Your Cat

Measure from your cat's belly to their shoulder, and your cat's width too.

I wanted a little extra room, but I measured one of the dogs to see how much room I had. I decided to make the door 7 inches high, and 6 inches wide.

Step 3: Remove the Door

If you remove the hinge pins, the door comes right off. I was able to remove both pins with a screwdriver and a hammer. Hang onto those pins. You'll need them to put the door back on.

Step 4: Find the Center

Measure the width of the door, and make a mark in the center.

Step 5: Find the Apex

Measure from the bottom of the door up about 7 inches, and make a mark. Hopefully, this mark intersects with the one you made previously. If you need to, redo the previous step to get the marks to intersect.