Hi jackiesakura,
Sorry I don't have a specific answer to your quantity question. However there have been discussions on the rice diet on this forum and perhaps someone who has gone through it might shed some light on it.
In the meanwhile, there is a thorough book on it where you can read more specifics and here:
"#7 Diet, An Accompaniment to Ohsawa’s Zen Macrobiotics"
you can read some more that might give you a fuller understanding of what it is you're embarking on.
Klara