Regardless if you are choosing side panels or functional drapery, it is best to have a drapery rod already chosen and preferably hung before measuring. When selecting a drapery rod, keep in mind it should extend at minimum 3" beyond the window casing allowing additional space for the panels to cover a portion of the wall next to the window. For example, a window measuring 36" wide from outside of casing will need a drapery rod that measures at least 42" (36" + 3" on each side of window). To make the window appear wider than it is, consider extending the drapery rod 8-10" beyond the casing if the wall space allows it. For example, a window measuring 36" wide from outside of casing could use a drapery rod that measures 56" (36" + 10" on each side of window) in order for the window to appear larger.