A. The reason that you got kind of a vague answer is that there is no specific amount of formula that all babies should be eating each day. While some infants may be eating just 24 ounces a day, others may need 32 ounces or more.
A good rule of thumb is that the average baby at this age is likely to drink about 5 to 6 ounces of formula every 3 to 5 hours.
The American Academy of Pediatrics, in the book Your Baby's First Year, also provides a nice guideline and suggests that 'on average, your baby should take in about 2 1/2 ounces of formula a day for every pound of body weight.' So for an average 3 month old baby boy who weighs 13 pounds, that would be about 32 1/2 ounces a day.
The AAP also states that 'most babies are satisfied with 3 to 4 ounces per feeding during the first month, and increase that amount by 1 ounce per month until reach 8 ounces.'
Keep in mind that these are still averages though, and some babies require more or less formula at each feeding and on each day. If your baby seems satisfied between feedings and is gaining weight normally, then he is likely eating enough.
If your baby is consistently eating more or less than these averages though, you might see your Pediatrician and make sure that you are recognizing your baby's hunger signals and that he is gaining weight normally.
As to when he is going to have his last feeding of the night, that is going to depend on your baby too. While some infants are already sleeping through the night by 3 months, others still need at least 1 feeding. If your baby is waking up and you aren't sure if he is really hungry, you can try to settle him down and put him back to bed and see what happens. If he won't go back to bed until he is fed or quickly wakes up again, then you likely need to continue with middle of the night feedings for a few more weeks or months.
Keep in mind that many people believe that reaching the milestone of sleeping through the night is more a developmental thing, and not necessarily related to hunger. That is why feeding cereal at bedtime often doesn't help a baby sleep longer.