Have you chosen the style of the rods you like? There's a standard rule of width to cover outside the window, but I don't recall. ;>P Six inches? I would get expandable rods, even though I hate the change of diameter showing. I have used the wooden poles so that they can be joined or trimmed. You will have so many interesting fabrics, wall coverings, and furniture the drapery rods won't be a feature to worry about. Hope someone else chimes in about set back on drapery. If you hang drapes too far out it looks strange, especially on the smaller windows, IMO. (Which isn't worth much).

These are the rods, they aren't extendable but custom size.

Belgian linen in this style

Scroll down a few questions on the attached link....she lists a few ways of looking at stack back....it depends on the thickness of the fabric...lined or unlined...and how the drape is created. For example, grommets will stack back much flatter than pinched pleats....

Here is a link that might be useful: ask an expert

Thanks, Annie!

If you have enough room on either side, just multiply the window by 1.3

mtn, glad someone else gave you some formulas. With each formula (multiply by 1.3 and divide by two---or add 12, divide by 6 & add to each side) you end up with double the stack back on the large window compared to the smaller window. This makes sense if you were to close the panels. If these are stationary panels you could choose your stack back per your preference. Is a workroom making the drapery for you, or are you buying ready made panels. Will your unlined linen show your dark window trim and wallpaper or walls?

Voila,

Answer - yes. In fact, i think the unlined panels look kinda cheap. I just ordered lined ones ....