Add the Bare Minimum
To determine the width of a valance for a 36-inch window, the Window Treatment Expert website suggests adding 2 to 4 inches on each side, adding less for narrower windows and more for wider windows. For a 36-inch window, this measurement would provide you with a valance that has a width of 40 to 44 inches.
Add More For Fullness
If you prefer a look that is full and bunched, you will need a wider valance. For a gathered, full effect, multiply the window width by 2 to determine the valance width. The valance for a 36-inch window, therefore, should have a width of 72 inches.
The size of your valance is based on your personal preference. If you prefer a sleek, tailored look, choose a valance of 40 to 44 inches. If you prefer a romantic, full look, choose a valance with a width of up to 72 inches. Keep in mind that a fuller valance will most likely cost more, as it has much more fabric.
Audrey Pannell has been writing since the year 2000. She has written for AOL and eHow. She holds a Bachelor of Science in public administration from the University of Texas at Dallas and also completed a certification course to obtain a teaching certificate for early childhood through fourth grade.