An inside mount requires at least 1.5" of depth. Measure the inside of the window frame from left to right then inside top to bottom. Click on link below picture to view measuring video.
And outside mount requires an additional 3" of length to account for the mounting hardware and the mounting block. The length and width measurements should go from outside molding to outside molding or simply whatever you would like the finished shade to measure. Click on the link below the image to watch the instructional video on measuring for an outside mount.