Hi!! I just peeked at a site and found this information:

Before measuring the length, decide whether you want your curtains to fit to the sill, below the sill or to the floor.

We suggest that:

Sill length curtains finish 1/2" (1.5cm) above the sill.
Curtains that fall below the sill finish 6" (15cm) below.
Floor length curtains finish 1/2" (1.5cm) from the floor.

I don't think it matters, evidently, but I would keep in mind the symmetry of the lengths ie: if other sills are hidden, hide them all. Your drapes are outside of the sides of the window, hiding the frames, right? Perhaps exposing only the sills would look like the drapes were too short?

I think, personally, that if curtains are inset, the entire frame is exposed, and if the curtains extend beyond the side frames, the sill should also be hidden, or they'd look too short.

Just MHO....;-)

http://www.thetextilemart.com/aa5.measure.html

Hi
Sill length drapery should be 4" below frame....
here is a site that will tell you all you want to know.

Betty

I got a swift response from SEWNEWS which really surprised me. They wrote, "All of these lengths are acceptable depending on the look you want. I like to make my curtains stop at the bottom of the frame. Curtains usually have about a 4" hem, and my goal is to not have it show in the window, and when the curtain is closed, it covers the window completely."

THETEXTILEMART, "The finished length on short draperies should be 4" longer than the bottom of the window.
Betty, I think these come out the same. The way I figure, 4" below the bottom of the window brings us to the bottom of the frame."

Glitter, I think your site would have the curtain fall 2" below the bottom of the frame. I suppose that would be okay, too.

Thanks guys,
Cove