The first step whenever making custom curtains is to take accurate measurements. You need to measure from curtain rod to floor or to the bottom of the sill, whichever you decide you want to do. In this case we are going right down to the floor. Then you need to allow for hemming. In this case, the bottom of the curtain will be the accent piece and it will measure 18″. So that 18″ doubled plus 2″ for a hem is added to the rod to floor measurement along with a 2″ top hem.