The window measuring guide for custom curtains is as follow:
There is no better way to update any room in your home with window treatments.
First, you have to see where you want to place the curtain rod.
If your window frame is anywhere from 48 to 86 inches wide, your rod is going to need a central bracket to support the rod.
To get the fullness; multiply the width of the window frame by two or even three to create gathered-looking drapes that will add a luxurious feel for your room.
For the length measure from the floor to the rod. Add an inch or two to the length if you want the drapes to gently touch the floor in the room.