If adding a door opening, be sure to consult a licensed contractor or structural engineer to confirm requirements for load-bearing walls and structural headers. The rolling track can be installed on the wall to the opening header or to the ceiling. For ceiling installations, also ask what blocking may be needed overhead to support the weight of the door. Start by measuring the width of the opening from outside of trim to outside of trim. For the height using a ceiling-mounted track, measure from the floor to the ceiling. For wall-mounted track, measure from the floor to the top of trim.
The final door size for a wall-mounted track should be the width of the opening to the outside of trim by the height of the door opening to the top of the trim minus 1/2 inch. The door size for a ceiling-mounted track should be the width of the opening to the outside of trim by the height of the wall minus the track and wheel depth, blocking and a half inch.