A system is provided for properly resizing a window shade (10) to fit within a window frame adjacent a window. At least one ruler strip (20) is provided with visible graduations (28) thereon. Indicia (29) are provided adjacent at least some of the graduations. The indicia are descriptive of a width of a window frame in which the window shade will fit when the window shade is cut at the graduation (28) adjacent to that indicia (29) . A position of the graduations (28) and the corresponding indicia (29) are misdescriptive of a width of the window shade so that clearance around the perimeter of the window shade and cutting of bothe edges (6, 8) of the window shade are accomodated. Both rectangular window shade and arched window shade sizing systems are provided. A retainer (30) is also provided for holding and guiding of a cutting tool (K) during cutting of the window shade for proper resizing.