Valances are used to cover the hardware that holds your curtains in place and can add a designer touch to a room. Determining the amount of fabric needed to make your valances is the first step in making your own valances. Depending on the valance pattern you have chosen, you may need more or less fabric than what is needed for a standard valance.
Measure the width of your current window treatment. Make sure your measurement is on the outside of the window treatment so that your valance is wide enough to cover the hardware currently installed. Write down this measurement and then add 2 inches to allow for the window covering's operating hardware.
Measure the height of the valance. Make sure you measure from at least 2 inches above any molding or hardware and continue to the bottom of the current window treatment. Multiply this measurement by 15 percent to find the correct length. Any longer and your window will look top-heavy; any shorter and your valance will seem out of place.
Look up your current treatment on a valance return chart to determine the return or depth of the valance. For a single-layer drapery, you'll need a minimum return of 5 1/2 inches, while a window with no treatment will need a minimum of 1 1/4 inches for the return.