I thought I'd post this for those beginners out there that do not own a scale for measuring grains out.
I don't own a scale myself, but the general rule of thumb that I follow is that 1 lb of grain works out to 4 cups by volume. (Or, 1 oz of grain works out to 1/4 cup.) *
1.00 lb = 16 oz = 4 cup
0.50 lb = 8 oz = 2 cup
0.25 lb = 4 oz = 1 cup
etc, etc, etc
* = Data obtained by dumping several different 1 lb grain bags from the LHBS into a 4 cup pyrex measuring cup and seeing that every one of them pretty much hit the 4 cup mark dead-on.