A Parent's Guide to Bottle Nipple Sizes

What bottle nipple size will work best for your little one? Find out what the different sizes mean, when to use each one, and how to tell if your baby needs a faster or slower flow nipple.

If you’re planning on bottle feeding your baby – or you’ve already started – you’ve likely come across different bottle nipple sizes. But which size will work best for your baby at different ages and stages? We’ve got you covered with our bottle nipple guide.

Number, flow, and age sizes: What do they mean?

Bottle nipple sizes indicate how fast milk or formula will flow from the bottle. The bigger the hole, or the more holes there are, the faster the flow.

Some companies will just name the speed that milk or formula will flow from the bottle: slow flow, medium flow, or fast flow. (There are also variable flow nipples, where you can adjust the flow speed as needed.)

But other bottle companies will use numbers to alert you to the different nipple sizes.

Often, bottle nipples will also have a suggested age for a baby to use the nipple:

  • Size 0 usually means that the nipple is designed for preemies. Sometimes, these nipples have a very slow flow, slower than the typical newborn size nipple. Other times, the flow is the same as the typical newborn slow flow.
  • Size 1 is a slow-flow nipple, appropriate for newborns and other babies under 3 months of age.
  • Size 2 is a medium-flow nipple, generally appropriate for babies 3-6 months of age.
  • Size 3 is a fast-flow nipple, generally appropriate for babies 6 months of age and up.
  • Sometimes, you might see size 4 nipples, with a very fast flow – appropriate for babies age 9 months and up.

You can usually find the size on the side of the nipple.

Generally, the faster flows are suggested for older babies, as they are usually able to drink more quickly and handle that faster flow rate.

But even though most bottle nipples suggest an age range, age isn’t the only thing that matters when making your choice.

Learn more about bottle nipple sizes in this video from New Parents Academy:

Every baby is different, after all! If they’re happy with the flow from their current bottle nipple, there’s no need to change the flow type, even if they’re old enough for a faster flow. Your baby’s responses and needs matter more – as we’ll go over in the next section.

When to use the different nipple sizes?

Although you’re free to use baby’s age as a guideline for when to change bottle nipple sizes, there are times when the size meant for their age isn’t consistent with what they really need. It’s better to watch how baby sucks milk or formula out of the bottle and adjust accordingly.

Slow-flow nipples are the way to go if your baby is under 3 months of age. This helps baby get used to the flow of milk or formula from the nipple.

But if baby is older than 3 months of age, consider how you’re feeding baby – and how they’re responding to the flow.

If you’re feeding pumped breastmilk

If you’re both breastfeeding and bottle feeding your baby pumped breastmilk, you’ll want to use a slow-flow nipple. That’s because slow-flow nipples mimic the flow of milk from your own body, and require baby to work to remove milk (just like they must do at the breast).

Give your baby a nipple with a faster flow, and they might start to prefer the bottle over the breast because it’s easier to get milk out of the bottle. This may lead to nipple confusion, where baby refuses the breast completely in favor of the bottle.

Generally, you should stick to the slow-flow nipple as long as you keep breastfeeding and bottle-feeding pumped breastmilk. (The exception is if you have a very fast milk flow, and baby gets frustrated with the slow-flow nipple because it doesn’t accurately mimic the flow from your own nipples.)

If you’re exclusively pumping, it’s also best to stick with a slower-flow nipple because a baby can generally digest breastmilk more quickly than formula milk.

When baby might need a faster flow

But what if baby is only drinking formula from a bottle – when to change sizes? Here’s how to know when it’s time for a faster-flow nipple.

  • If baby takes over 25 minutes to finish drinking from the bottle, or gets hungry quickly after not drinking much, it’s probably time to move to a faster-flow nipple.
  • Harder sucking, flattening the nipple, and sucking fast without many swallows are other signs that baby should graduate to a faster flow.
  • And if they’re kicking, squirming or fussing, or they fall asleep during a feed, they might be getting impatient with the slower-flow nipple and should move up.

When baby might need a slower flow

You might also need to move baby down to a slower flow.

Baby might need the flow slowed down if:

  • They gulp a lot
  • They swallow hard
  • Their stomach gets upset after feeding
  • They gag or spit up often
  • They cough during feeds
  • They turn away from the bottle or refuse to eat
  • They choke
  • They show reflux-like symptoms
  • They seem gassy, squirmy, or uncomfortable after feeds

Keep in mind, though: Sometimes, these symptoms are caused by something other than a rapid flow of milk or formula. Baby might be sensitive to an ingredient in formula, or to something you ate if you’re feeding pumped breastmilk. They might also have gas buildup.

What else to consider with bottle nipples?

Size isn’t the only thing that matters when it comes to bottle nipples. Be sure to consider these tips as well:

  • Make sure that your bottle nipple has an anti-colic valve, to keep baby from swallowing too much air.
  • If baby is both breastfeeding and bottle-feeding, choose a bottle nipple that mimics the size and shape of your nipple.
  • Nipples should be replaced if they’re worn or weak, as baby could choke on them. If the nipple thins out, changes color, cracks, breaks, swells or gets sticky, it’s time to get a new nipple.

Introduce Allergens Safely and Easily with Ready. Set. Food!

All health-related content on this website is for informational purposes only and does not create a doctor-patient relationship. Always seek the advice of your own pediatrician in connection with any questions regarding your baby’s health.

These statements have not been evaluated by the Food and Drug Administration. Products are not intended to diagnose, treat, cure or prevent any disease.  If your infant has severe eczema, check with your infant’s healthcare provider before feeding foods containing ground peanuts.