That all depends on what you have in your scene... as well as how much subdivision might be used. If you want to get a feel for it, open task manager before you call Reality, then watch the memory use in the processes tab of the Luxrender.exe as it parses out the scene file; you will see the memory usage go up, and eventually the lux render window will appear. Check your scene set to a small size and see... I ended up fitting 32gb ram, but most of the time its because I might be running several smaller test renders at the same time. If you look at the memory usage in this way you should get a good feal for what happens to memory usage if you add complexity / subdivision / image size. The one thin you don't want to do is have a scene that takes more memory than you have, as if it starts to use a disk swap file, the render speed will slow down by massive amounts...

Basically the more memory you have, the bigger and more complex scenes you can render. There are ways of conserving memory usage, I'm sure Paolo or someone can give a more expert view on this! `¬)

P.S. as far as physical size goes, it depends on what resolution (pixels per inch or dots per inch you want? - screen size or print size)

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