The length and width of a window are two things you need to measure for a customised curtain. Let’s start with the width where the thing to consider is your preference for the curtain’s fullness. You measure the width of the window and multiply it with two if you want standard fullness, and multiply it with two & five-tenths or three if you want more layers in your curtain. Next is the length that can be the same as the length of the window known as sill length. If you want it to be hanging more, consider apron length that is longer than the window sill, or floor-length, or extra long that touches the ground.