I have another store called patternspatterns where I sell some of my unused stash. Any piece 3 yards or less I list as one piece. Anything over that I list the total yardage, but sometimes mention that I will cut it, depending on the fabric.
Also, I finally bought a digital kitchen scale for about $30, because I was having trouble guessing the weight. The weight can vary due to the weave, finish, etc. I have had a few international fabric customers, and was often way low on what I listed for postage. Another thing about international sales, there are some coutries that do not allow certain materials, including fabrics, into their country so you might want to check that before you ship to another country. You can go on the USPS website to see what a particular country might reject. Good luck.