A common rule for displaying curtains properly says the curtains finished width should be at least 2 times the width of your window (if not more - sheers can be 3 times the window width) to achieve a look of proper fullness.

Do you need two curtains per window?

Most often you see two panels per window, but if your window is small, you can easily get away with one panel. ... Your curtain should sit four to six inches above the window. The panel width should be two to three times the width of your window or door.

Can you put 3 curtains on a window?

Pull back two adjacent panels of the three curtains into a tie-back, creating a left-to-right or right-to-left swoop on the window, depending on your window hardware. Let the third curtain hang gracefully down the other side of the window or gather it with a tie-back of its own.