How much should a 10 day old be drinking? Her feed is about 2.5 hourly apart. And her intake ranges from 100-120ml depending. Is it enough?

Most of my friends are breastfeeding and feed on demand. As long as their babies are gaining weight, they are not too worried about the actual amount that their babies are consuming. After the initial week where a baby's weight will decrease, the baby is expected to return to his/her birth weight by the second week. From third week onward, the baby should start gaining weight.