Measure the width of the doorframe of the closet. Hang the tension rod in the frame, and measure the height from the top of the rod to the floor.
Cut a piece of fabric that measures twice the width of the doorframe. The length of the fabric should be the height of the closet plus 6 inches.
Fold the sides of the fabric over 1/2 inch, and press with a hot iron. Fold another 1/2, press and then pin.
Stitch along the inside edge of the folded sides.
Fold the bottom edge of the fabric up 1/2 inch and press. Fold up another 1/2 inch, press and pin in place.
Sew along the bottom edge of the fabric with a 1-inch seam allowance.
Fold the top edge of the fabric down 1/2 inch and press. Fold it down another 4 inches to make a pocket for the tension rod. Press and pin, and then stitch along the inside edge.
Pull the tension rod out of the closet doorframe. Slide the curtain onto the rod through the pocket. Hang the curtain and rod in the door of the closet. Gather the curtain so that it hangs neatly.