4 oz vs. 8 oz Baby Bottles: Which Size Do You Actually Need?

When I was building my first baby registry, bottles felt like one of those things I needed to stock up on. There were 2 oz bottles, 4 oz bottles, 8 oz bottles, glass bottles, plastic bottles and somehow I was supposed to know what my baby would actually use before he was even born.

After bottle-feeding two babies, my approach is much simpler: start with a few 4 oz bottles and wait on the 8 oz bottles.

The Short Answer

If you're wondering whether to buy 4 oz or 8 oz baby bottles, I recommend starting with 4 oz bottles for a newborn. Once your baby is regularly drinking more than 4 oz at a feeding, switch to the 8 oz size. Do not stock up on both sizes before your baby arrives.

That is what I wish I had done the first time.

Do Newborns Need 4 oz or 8 oz Bottles?

For a newborn, I prefer 4 or 5 oz bottles.

Technically, you could put a smaller amount of formula or breast milk into an 8 oz bottle, so you don't necessarily need the smaller size. But the smaller bottles are much more practical at that stage. They are easier to hold and take up less space during those early feeds.

When Should You Switch From 4 oz to 8 oz Bottles?

I wouldn't base the switch on a specific age. I would base it on how much your baby is actually eating.

Once my daughter started taking more than 4 oz at a feeding, I switched her over to our 8 oz bottles. It was that simple.

You don't need to switch just because your baby reaches a certain month or because a baby-feeding chart tells you that you should. If your smaller bottles are still comfortably holding your baby's normal feeding, keep using them. When they're not, that's your sign to size up.

My two babies moved up at completely different times. My first was drinking more than 4 ounces pretty early, so I switched him to 8 oz bottles when he was around 4 to 6 weeks old. My second did not move into 8 oz bottles until closer to 4 months.

That is why I pay much more attention to how much your individual baby is eating than to an age recommendation.

The transition itself was also much less significant than I expected as a first time mom. We kept using the same bottle brand and nipple, so as far as my babies were concerned, not much had changed. The bottle was just bigger.

One useful thing a week.

Practical tips, favorite finds, and shortcuts from pregnancy through the toddler years. Like a mom friend who's already done the research.

How Do You Know Your Baby Has Outgrown a 4 oz Bottle?

For me, there was no complicated sign to look for. Once my baby wanted more than 4 ounces, it was time for the bigger bottle.

I did try putting around 5 ounces into my 4 oz bottles, and in my experience, they tended to leak when I filled them that high. There may technically be some extra room at the top of certain bottles, but trying to stretch the smaller bottles was not worth it for me. I just moved up to the 8 oz size.

You also do not need to wait until your baby is drinking a full 8 ounces. An 8 oz bottle simply gives you enough room as feeds get larger. My daughter uses 8 oz bottles even though most of her bottles contain about 5 ounces.

Can You Use 8 oz Bottles From Birth?

Yes, you can use 8 oz bottles from birth. You don't have to fill an 8 oz bottle all the way, so if you want to skip smaller bottles entirely, that's an option.

Personally, I still prefer starting with the smaller bottles. They're convenient during the newborn stage, and more importantly, buying only a few smaller bottles gives you a chance to figure out whether you and your baby actually like that bottle before investing in more.

A bottle can look perfect when you're building your registry and then simply not work for your baby. If you've already registered for a full collection of that brand in multiple sizes, you're left with a lot of bottles you may never use.

Does Switching to an 8 oz Bottle Affect the Baby?

In my experience, no. If you keep the same bottle system and nipple, your baby may barely notice. The bottle is simply larger.

I think about bottle size and nipple flow as two separate decisions. If you are wondering whether it is also time to size up the nipple, here is how I knew when to change bottle nipple flow with both of my babies. Moving into a bigger bottle does not necessarily mean your baby needs a faster nipple at the same time.

What to buy and register for

If I were starting over, I would register for about four 4 oz bottles in the brand I wanted to try. I would skip 2 oz bottles entirely and would not register for a big set of 8 oz bottles yet.

Once I knew my baby liked those bottles and was approaching the point of needing more than 4 oz at a feeding, I would order about four of the larger size in the same brand.

For the larger size, four 8 oz bottles is plenty for most families. My daughter eats about five times a day, and we wash bottles throughout the day, so four works for us. If you would rather wash bottles only once at the end of the day, you may want five or six instead.

This is the same less-is-more approach I use for the rest of a baby registry. You do not know which bottle your baby will actually like yet, and there is no reason to own eight bottles your baby might refuse.

Two more things I would cut back on. I do not think 2 oz bottles are worth it, because the stage when they help is so short that you can simply put a smaller amount into a 4 oz bottle.

And on material, I started with glass for my first baby, but as he got older and wanted to hold his own bottle, glass became impractical (they can fall and break), so I switched to plastic. That is personal preference, and I go deeper in my post on glass vs plastic baby bottles.

Should You Keep Your 4 oz Bottles After Switching?

I would not get rid of them right away. I still keep two 4 oz bottles even though my daughter takes her regular feeds from 8 oz bottles.

I use the smaller ones for allergen introduction with Ready, Set, Food!, so I can make sure she finishes all of the powder before the rest of the feeding. I also use one for her vitamins. Because she was born prematurely, she takes iron and a multivitamin, and I would rather put those into a small amount of formula I know she will finish than mix them into a full bottle and risk leaving some behind.

Not every baby needs vitamins or powdered allergen introduction, so you may eventually have no reason to keep the smaller bottles. I would still hang onto one or two at first.

Baby Bottle Size FAQs

When should I switch from 4 oz to 8 oz bottles?

When your baby is regularly drinking more than your smaller bottles comfortably hold. I would go by intake, not age. For me, that meant switching once my daughter drank more than 4 oz at a feeding.

How long do babies use 4 oz bottles?

It varies a lot. One of my babies moved to 8 oz bottles around 4 to 6 weeks, while my other kept using 4 oz bottles until around 4 months.

Can a newborn use an 8 oz bottle?

Yes. You can put a small amount of milk or formula into an 8 oz bottle. I still prefer smaller bottles for the newborn stage because they're more convenient and allow you to test a bottle brand before buying the larger size.

How many 8 oz bottles do I need?

I recommend starting with about four if you are willing to wash bottles during the day. If you want enough bottles to get through a whole day without washing any, you may prefer five or six, depending on your baby's feeding schedule.

Should I register for both 4 oz and 8 oz bottles?

I would not. I would register for about four 4 oz bottles, make sure your baby likes that bottle system, and then order the 8 oz version when you need it. This avoids ending up with an entire set of larger bottles your baby will not take.

Disclosure: This post contains affiliate links, which means I may earn a commission if you purchase through my links, at no additional cost to you. As an Amazon Associate I earn from qualifying purchases.