My room is 13.5 X 20 and I have two rows. It might be a real squeeze to get two rows in like the other posters have said, but that is also dependent on how close your front row is. I have a 114" screen and my front row is about 10 feet from the screen. I have a rear entrance to the theater so I had to leave a walkway at the back.
On the chairs, my front row is three wide and the rear is four wide, two on the ends and love seat in the middle. This still leave a small walk way on the side.