got your pm, and responded. I'm not sure on the exact dimensions.. but I had 2 pieces in my 55 gallon. I'm sure you could find a pic if you went through my threads..
like i said in the message though, if you have a 40gallon breeder tank it'll fit I'm guessing that it's wider than a 55 gallon.. but it'll take up most of the space in the tank ... I had this and a larger piece that i gave to varanio (sp) in my 120 gallon and it looked great.