A room without window treatments is not completely decorated. Window treatments help set the mood of a room and can look either formal or relaxed, depending upon the style of the treatment and the fabrics used. Waterfall valances look like water cascading from the top of the valance. The fabric covers up about one-third of the total height of the window, but the fabric itself may be about three times that measurement. Determining how much fabric you'll need for your waterfall valance is a simple process that should only take a few minutes.
Measure the outside of the window casing, from the left outside edge of the windowsill to the right outside edge of the windowsill.
Measure the height of the window from the top of the window casing to the bottom of the windowsill.
Multiply the width of the window casing by three. This gives you the total width of the fabric you should use for the window. This is the measurement for the centre waterfall part of the valance only.
Divide the height of the window by three. This gives you the total height of the fabric you should cut for the window.
Take measurements for each window you wish to cover with the waterfall valance. This allows for variances in window sizes and ensures your measurements will be correct.
Determine the measurements for the side panels of the window treatment by measuring from the top of the windowsill to the floor and add 1 1/2 inches to this measurement to allow for the hem. If you prefer the panels don't go all the way to the floor, adjust your measurements accordingly. This is the height measurement for the side panels of the window treatments only, not for waterfall valance part. Depending on how full you want each panel to look when pulled back, you may want the valance to be about the actual width of the window or a little less.