My little girl would only take about 6 oz at a time maybe 3-4 times per day. Each baby is different and they will only take what they want. Don't stress over it too much if you are, they will drink/eat when they are hungry. My daughter is one now and will eat and drink when she wants. Will turn her head when she is full.
Thay are all different. I asked my doctor the same queation. She sadi as long as they are well established on solids there isnt really a minumum. They know what they need. When i asked her for a range she said 16 to 30oz in 24 hours.