To find width:
Measure the width of the area to be covered at the place where the headrail will be installed to the nearest 1/8″. Blind should overlap opening at least 4″ on each side to ensure privacy.
To find length:
Measure the length of the area to be covered and round down to the nearest 1/8″. Blind should extend at least 3″ above opening or window molding. For ceiling-to-floor installations, deduct 1/2″ for proper clearance. Specifying OB measurement means the factory makes no deductions allowances. To ensure easy access through the door and allow adequate overlap, consider the stack width.