how much cereal is too much?

Theresa
My baby is 4 months and we just started rice cereal. She loves it. We are giving her it in the morning and then again before bed. Only about 1-2 tablespoons of it. She also drinks about 40oz of formula everyday. I don't want to over feed her but I also want to make sure I am giving her enough food. Any suggestions/opinions on what you do?