To get the right length, measure from the floor to where your curtain rod will be mounted, keeping in mind standard curtain lengths: 63, 84, 96, 108, and 120 inches. A general rule of thumb is to hang rods 4 to 6 inches above the window frame to create the illusion of taller ceilings. Curtains should extend 3-6 inches beyond each side of the window for full coverage. For a luxurious, full look, use curtains that are twice the width of the window.