If you have planned to install the outside mounted blind, you will have to cover the whole window space. Therefore, measure the entire window frame and coordinate with the window treatment company to provide appropriate size window treatment.
If you want to mount the window treatment inside, you will have to measure the space within the frame. At least, take three measurements in each direction. Horizontally measure the window's top, middle, and bottom area because the windows are not often evenly spaced.
