How big can red-eared sliders get i'd like my two to be medium-sized.?

add images if you can(please.)!

How big can red-eared sliders get i'd like my two to be medium-sized.?
over a foot long, they get to a decent size


http://www.newsday.com/media/photo/2003-...


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http://www.samford.edu/schools/artsci/bi...
Reply:kinda big like mabie like a foot long i think



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