When I have made tablecloths for home use, I have allowed a 10" drop, because I don't like dealing with fabric in my lap, but I think a 12" drop would be fine. I wouldn't want more than that though. If you are setting up a table for serving, or just to display something, I don't think it matters how long the drop is. I have seen them all the way to the floor when they are not for seating.