First, I just want to say that this is a highly customized project, so I'm not going to provide you the measurements we used. It is all going to depend on what type of window you have, and you need to measure your own window anyway, to make sure you have as tight of a fit as possible. This is the 3rd of these types of custom window doors we've made (scroll all the way to the bottom of this post to see past iterations) and each one has been different, but all were based on the same principals.
Which are, make it safe for the cats, and make it so nobody can break in through it. Obviously, if someone wants to break in, they're going to do it, and can just break a window. But you don't want to make it easy for them to get in through the cat door in the window (and by the way, we know for a fact that someone tried unsuccessfully to break in through our very first cat door back in California, but they couldn't, so they broke windows instead).
Also, I should note that this is only stage one of our cat door. This design is fine for spring and summer, warmer months, but we are going to beef it up a bit come fall, to help hold in the heat for winter.
