Also, I don't have my original cup with my rice cooker. I'm putting 2 cups water in the basin and it makes the cooker cook for about 45 minutes. Then it flips to a warming phase.
I usually double the rice with water inside the cooker, and add just a little extra water for whole grains.
Do you think that's the correct amount of water above and below for a batch of mixed grain?
Since I first posted this I made a search and found the instruction manual for my rice cooker. So I can confirm that the little cup that came with it is 180ml, just as serenity posted. It's pretty easy to find measuring cups -- even here in the US -- that have milliliter markings along with the English measurements.
With that in mind, I can offer some ratios from my cooker instruction manual. Remember, "cups" means "180ml" in this context:
2 cups rice -- 2.5 cups water
3 cups rice -- 3.5 cups water
4 cups rice -- 4.5 cups water
5 cups rice -- 5.5 cups water
6 cups rice -- 6.5 cups water
7 cups rice -- 7.5 cups water
8 cups rice -- 8.5 cups water
So basically they are recommending a one-to-one ratio of rice to water, plus 90 milliliters of water. 90 milliliters is about 6 tablespoons.
Now, when I follow their recommendations, my cooked grain mix always comes up fairly dry. I like it that way, but when I'm cooking 6 or 7 cups of grain, I usually put in an extra full cup of water. If I were making two cups of mixed grains, I'd use 3 cups of water total. (That's true whether we are talking "rice cooker" 180-ml cups or standard US cups.)