i've once read that baby should drink her weight x 2.5-2.7 (a factor). eg, if baby is 12lbs, 12 x 2.5=30, she should drink total of 30oz in a day.
my bb weight 12.5lb. she can only drinks 20-25oz a day. on average, 3oz per meal. but sometime 1 or can be 6! i think if she gain weight probably, has enough or good poo poo and pee pee, and is happy all the time, thats ok.