Seems simple enough, right? It is but there are a few steps you need to take in order to ensure the proper fit. Obviously, you need to measure your window’s width from casing to casing. Then you should add approximately two to five inches to the total width, depending on how much of the wall you would like covered. Buying an adjustable rod helps with this also. Not only does it allow for measuring mistakes, but it also can add drama and width to the window.
Also, you need to take into consideration the fabric choice of your curtains. If they are heavy, thick curtains then obviously you need a heavier rod and brackets. Alternatively, if you have sheers, they will be okay on any type of rod.
One last thing to consider is the top hem of the curtain. It needs to be wide enough to slip into the rod.