Just got back from the install, It's from Webasto and the opening is 18" by 391/2". It has two presets so if you like it opened only half way, you hit one of the presets and thats where it will open to every time. It all so closes automatically when the key is shut off, if you want to leave it open just hit any button and it will remain open. I had the storage console on the roof and as you can see they cut it off and made up a little endcap made out of the headliner material. Awesome job, I love it!!