Here are a few pictures of my tray. Regular size pads work well in it but I recently decided to go with the adult size pads they work even better (more coverage) As you can see it was just "used" before I took the first shot.
Anyway, this is Mo demonstrating the funny part about it is he doesn't use it as he is housebroken.
I did a rough measure and it is approx 30x29 or 30x30. I keep it in my laundry room.