Many factors can be involved in determining the correct length of a drapery rod, however here are some of our recommendations. The term stack back refers to the width of a drapery panel when in the open position. Typically the panels should not block your view out of the window, when in the stack back/open position.
For instance, a 31 inch wide window may require 3 to 6 inches past the window molding on each side to avoid blocking the view. A 96 inch wide window may require 8 to 12 inches past the window molding on each side to avoid blocking the view. It is all determined by the window width and how much additional space is needed to avoid blocking the view/window.