Just plain rice ? Then you can store that for at least a week and keep eating it, actually, it probably is safe for a very, very long time, as long as you don't have meat or anything else that can spoil in it.
If you have the current cup, then just fill that up, and dump it into a normal measuring cup, and see how much it holds if it don't say anything on it, itself.
BTW, I don't understand the need for a rice cooker, it is 1 cup rice + 2 cups water and it can't be easier to cook rice on the stove. Bring water to a boil, dump in the rice, reduce heat to simmer, cover it, and leave it alone for 30 mins. Never had any issues, and the rice is perfect every time.