Read this technical novel by Kevin and you will understand a great deal more about turbos:
http://www.automotiveforums.com/vbul...d.php?t=156363
Trim= [(inducer squared)/(exducer squared)] x 100
...where the inducer size is the turbo inlet side of the wheel (usually in mm), and the exducer size can only be seen, as Kevin says when the wheel is not inside the housing (also size in mm).
So trim has no relevance to the sheer SIZE of a wheel, rather to the ratio. Read the article, it is terrific!