The tank:
The tank is 20gal total with approx 15 gal of display room. The dimensions are 24" long X 12" wide (8" in display, 4 " behind separating wall") X 16 " high. I purchased the tank used. There is a wall in the back 1/3 of the display for the HOB skimmer, heater, and whatever else i end up adding to the tank. Here is a picture to give you a better idea of the overal shape
(note: done on goggle sketchup: