Remove doors using a screwdriver to make carpet installation easier. Set the doors in another room.
Unroll the carpeting pile side down for cutting. Measure the longest wall of the room and the width of the room. Add 6 inches to the measurements. Cut the carpet according to the measurements with a utility knife.
Turn the carpet over. Make sure the pile is facing the same direction as the carpeting in the next room, so that the carpeting visually transitions at the doorway. Adjust the carpet to ensure that any designs flow from the room to the next at the doorway. Press the carpeting against any crown molding in the doorway and cut any excess carpeting.
Cut a piece of seaming tape to fit the doorway. Lay the seaming tape adhesive side down. Melt the adhesive with a seaming iron. Press the carpeting on top of the tape, so that the carpet butts tightly with the carpeting from the next room.
Roll over the seam with a rolling pin. Allow the adhesive to dry for 30 minutes before attaching the rest of the carpeting to tackless strips.