same dimensions as a movie screen?
All the monoliths are black, extremely flat, non-reflective rectangular solids whose dimensions are in the precise ratio of 1 : 4 : 9 (the squares of the first three integers). These dimensions are the main source of debate about the simple external design of the monoliths. It is suggested in the novel 2001 that this number series does not stop at three dimensions.[1]
The monoliths are observed in several different sizes - TMA-0 and TMA-1 are both about 11 feet long and TMA-2 is two kilometers long on its longest axis, whereas the monolith that appears on Europa is considerably larger. They may be able to assume any size, because in 2010: Odyssey Two, the Star Child, created from the astronaut Dave Bowman, cryptically notes that the monolith is actually one size - "as large as necessary".
http://en.wikipedia.org/wiki/Monolith_(Space_Odyssey)