There is sometimes some confusion regarding plus size models. Lot’s of ‘Plus Size’ models don’t wear plus size clothes.
Here in the US you can generally find ‘straight sizes’ up to a size 14 US in any store you go into. Plus size clothing generally starts around a size 16 US.
'Straight Size' models wear sizes 0-4 US, and 'Plus Size' models wear sizes 6 US- up.
So while plus size clothing starts around a size 16 US, ‘Plus Size’ models are just any model that fall above the ‘straight size’ range. The average US woman is a size 14, so lots of plus size models are actually smaller-than average women and are not considered ‘plus size’ outside of the modeling industry.
There is a lot of dissension in the plus size community regarding this contradiction, see Plus Model Magazine: Plus SIze Bodies, What Is Wrong With Them Anyway? for more on this issue.
Side note: one of the most successful straight size models of all time, Cindy Crawford, was a size 6 US during her modeling career, which in todays ranges would put her in the plus size model catorgory!