Measure the width of the window, then the length you desire.  You may choose to place panels just to touch the windowsill, sit under the windowsill or go to the floor.  It is all about personal preference.   Tiers are measured from the middle of the window to the windowsill.    Most of our curtains are 60" wide with some exceptions.   If your window is wider, you may require more than one curtain to get the desired fullness.   Our swags are split to accommodate an additional valance if extra width is needed.   Valances can also be hung next to each other for the desired fullness.  

Curtains have a 1-1/2" header and 1-3/4" rod pocket.  

It is recommended that curtains be 1.25 - 2.25 times your window width. 

How many curtains will I need? 

Fullness is a matter of personal preference.  We recommend 1-1/2 to 2 times the width of your window  measurement.   However, we have used less if we wish to see more of  the pattern.   You may use 2 or more times the width of your window if you would like a fuller look.