It is 48'' by 22''. I suggest that instead of having dedicated buttons for the trackball, just use the ones from p1 or p2 for mame, and then make some of the admin buttons for mame the mouse buttons. My trackball buttons are the two black ones all the way at the top, one of them is pause and the other escape in mame, but they act as regular mouse buttons if i need an emu that needs them or when i am navigating windows. Show us when you get started!