NOTE: Use the EDGE of the Exterior Casing as your measuring point (DO NOT USE THE BLIND STOP). Spencerworks All-Season Hanging Windows™ mount flush against the outer edge of the blind stop. The height of the window is equal to the longest dimension of the exterior casings outside edge minus 1/8”.
NOTE: When ordering windows oversized for trimming added 1/4″ to the width found in step one. If you feel that your situation requires more than 1/4″ of extra material in the storm window it may be necessary to repair your homes exterior casing to achieve a perfect fit.