I believe that British sizes run slightly differently, but in American sizing, 16 is the largest that is considered "regular." Anything above that is considered a "plus" size.
To put sizes in perspective, the average size of most actresses today (Jennifer Aniston, Lindsay Lohan, Angelina Jolie) is a very petite two. Marilyn Monroe was a size 12, which was considered sexy and curvacious in her day, but would be positively porky by today's show business standards. Of course, there is a vast difference between Hollywood and real life.
