We always ask our clients, "do you care what way your drapery "stacks" when you pull the drapery back to let the light in?" Also, a client might have a view they don't want blocked. This matters because when you close the drape, the fabric that "stacks" together can block a view or a certain amount of space.
Once you know if you have any elements that will rule what way your drapery has to stack, you have to decide wether to make the drapery either center-draw (two panels of drapery, separated in the middle) or one-way panel (drape is only one panel and closes either to the left or the right, sometimes they can close both ways if specified but it is still just one panel).
After deciding what way the drapery will stack, you can get an idea of how much space you will use for stacking. We must keep in mind that the wider the window/width is, the more stacking there will be due to the fullness and amount of fabric needed to cover the windows. Also, if the fabric is heavy/thick, it takes up more space when drape is closed and fabric stacks together.
If you need to know how many inches your drapery will stack back, it is hard to find out an exact number due to the fullness and kind of fabric used but here is a formula that the workroom uses so it can give you an idea.
For a one-way panel use:
Width of Rod/(divided by)2.5= Inches of stack back
For center-draw/pair drapery use:
Width of rod/(divided by)5= inches of stack back on each side
If you have any questions regarding stacking please feel free to contact us to help you.