The shade is mounted inside the window opening for a clean, tailored look. When selecting your width and height measurements, enter the exact dimensions of your window opening. Do NOT enter the size of an old/existing shade. The factory will make a 3/8" deduction off the ordered width for a proper fit (+/- 1/8" possible variance). Please make sure your window meets the minimum inside mount depth required to accommodate the brackets, or the flush mount depth if desired. Depth requirements can be found on the product page.