I have a tupperware pitcher, and it holds 3 pounds, when filled to the tippy top. It says "10 cups" right there.
Also, a completely full sour cream/cottage cheese container (the 16 oz size, I think, the one most people seem to have), holds one pound of grain, when completely full.
I hope that helps. If not, I can run to the basement and weigh a cup if you need me to!