I'd go with yardage - but I prewash everything, and a 10" layer cake does not end up 10" after washing. In fact, they don't even come out square after being washed. Find it interesting that one direction shrinks up more than the other . . .
Your shop hop sounds real fun! I'm taking June 21st and 22nd off work, and DH and I are going to hit many of the shops in SD. Last year was the first year any shops in SD participated (15) and this year there are several new ones, so that is what I'm after this year.