Mainly we need the width and the height of the window treatment. Rule of thumb: for the width of the window treatment, add at least 10 inches to the window width, or up to 30 inches if the wall space allows; for the height of the window treatment, measure from where you want to hang the curtains down to the floor. (from several inches above the window frame up to several inches below the ceiling). This way we can make sure that the window frames can be fully covered by the window treatment.
Celuce