Bottles come in different sizes ranging from 2 oz (60 ml), to 8 oz (240 ml), or larger. So, which size do you purchase? Newborns and young babies do not drink very much, so a small bottle can be used. However, if you like the feel of a larger bottle in your hand, or these are the only bottles sizes you have, you can always put a small quantity of milk into a larger bottle.
But remember, before purchasing a bunch of any bottle type, make sure your baby feeds well from that type. Pick the type of bottle your baby does well on, THEN select which bottle sizes according to the options you have.
As your baby takes more milk per feeding, your baby will outgrow the smaller sized bottles. This is the time to trade in your small bottles for larger ones.
Some mothers worry about other people feeding their babies too much milk when large bottles are used. Because obesity due to over-feeding is an associated risk of bottle use, this is a valid concern. You can reduce the risk of over-feeding by supplying a bottle size that closely matches the amount your baby drinks.
For mothers who are pumping, choice of bottle size may be influenced by pump fit and/or storage needs. Many mothers pump directly into the bottle they are going to feed the baby from, making medium-sized bottles a practical choice for healthy, term babies.