These days with the thicker mattresses being 15"-18" thick, I think one needs to consider the bed it's going to be used upon. I like the quilt to hang 3 inches past the top mattress, I think anything goes...whatever a person wants.

this is how i do also. i measure top of mattress, the drop i think looks best and center the main design or it's border to come to edges of the top matress.

I have always preferred to have 12"drop too. I made a queen size quilt for my best friend and she was NOT happy with the length. I ended up making her a King size quilt for a queen size bed. We were LUCKY because I barely had enough fabric!!

I feel that a quilt is not a bedspread, so I prefer for it NOT to hang to the bedskirt or bedrails. I prefer about a 4"-6" drop since I also don't have to "share" my quilt with another body in the bed. :o :D

Jan in VA