After we were discharged from hospital and came home, I have noticed my little one had was constantly hungry; he would get tired very fast and not finish his meal. Around the same time, my milk supply dried out and I had to start using formula milk. Because he was feeding on demand, initially, I didn't pay attention to his daily intake. It was soon afterwards I started monitoring daily formula milk intake, when I have noticed the formula we've bought has already finished. My baby boy was having about 700 ml a day. To my surprise, by 3 months actual, he was having between 900 ml to 1100 ml a day.
So how much should a baby eat? Up to 6 months of age (if your baby is premature, like mine, 6 months corrected) the formula intake should be between 150 to 200 ml per kilogram per day (150-200ml/kg/24h). So lets say your little one is 8lbs (3.63 kg) - the formula milk intake within 24 hours should be between 545 - 726 ml. Use this calculation as a guideline only. Sometimes your baby needs to eat more (like mine did) to catch up and gain strength. If however you're concerned, do speak with a doctor and ask for medical advice.
If you're breastfeeding, the milk intake doesn't have to be monitored (as long as your little one is gaining in weight) and it should be until your little one is done latching (he/she had enough).
How often should baby eat? I feed mine on demand (started doing this as soon as we came home) - he eats when he's hungry; but I know other moms choose to stick to the hospital schedule (feeding every 3 hours).
What about "hungry baby" formula? From our experience, I would not recommend it. I have tried it and my little one didn't digest it properly and it didn't help him gain in weight either.
After 6 months (corrected if preterm baby), when you start weaning, the amount of formula milk intake changes.