When Should You Switch Nipple Sizes on Your Baby’s Bottles?

Is your baby starting to get frustrated with the bottle and you’re wondering if maybe you need to go up a nipple size? How do you know when it’s time to make the change?

Nipple size is just one of many choices when it comes to your baby’s bottles. Choosing the right size nipple for your baby will make feedings much more comfortable for baby and more enjoyable for everyone involved. But how do you know which is the right size nipple for your baby and when you need to move up a size?

In this post, we will discuss the preferable nipple sizes for formula fed and breastfed (including exclusively pumping) babies, signs it may be time to move up a size, and other reasons your baby may be fussy at the bottle.

When Should I Switch Bottle Nipple Sizes?

The nipple size you use for your baby’s bottles will depend on if they are formula fed or breastfed, their age, and other readiness cues.

For a Formula Fed Baby

For formula fed babies, there is usually an age guide for nipple sizes (flow) that come with the bottles. The manufacturer should have this guide posted on their website if it didn’t come with the bottles or you no longer have the package insert.

Related Reading: Which Avent Nipple Size Should You Be Using?

The faster nipples are meant for older babies, because they eat more at each feeding and are more capable of handling the flow of milk. Most manufacturers follow this guideline:

  • Slow flow: 0-3 months
  • Medium flow: 3-6 months
  • Fast flow: 6-12 months

However, age isn’t always an exact determinant of nipple size, as all babies are different. There are other signs, other than age, that will indicate that your baby is ready to move up a size, such as:

  • Sucking hard
  • Flattening the nipple
  • Getting aggravated (squirming, kicking, pushing the bottle away, etc.)
  • Smacking at the bottle
  • Taking forever to feed (30 min.-1 hour)
  • Eating less at feedings, but getting hungry again soon after

If your baby isn’t showing any signs of frustration and isn’t taking forever to eat, then there is no need to move up a size. But if your baby is showing some of these signs, go ahead and give the next size up a try and see how your baby does. It’s all about trial and error.

If you do move up a size and your baby is gagging, coughing, choking, or dribbling milk out of the side of her face, then the nipple flow is too fast, and you will need to go back down a size. You may also need to move back down a size if your baby is exceptionally uncomfortable shortly after feedings, as the fast flow may have been too much for her digestive tract (source).

For a Breastfed Baby

Experts recommend using slow flow or “newborn” nipples when bottle feeding a breastfed baby. Typically, you should never have to move up a nipple size for a breastfed baby.

This is because breastfed babies have to work for their milk when at the breast, and breasts usually release milk much slower than a bottle nipple. If you give your breastfed baby a nipple where their milk just flows right out, they may start to get lazy or even refuse the boob. Essentially, the bottle flow should reflect flow during breastfeeding.

It’s also effortless to overfeed a breastfed baby when bottle feeding, so caregivers should be sure to mimic breastfeeding as much as possible and feed baby in a more upright position, change positions midway through, and practice paced bottle feeding.

Even though most breastfed babies should never have to move up a nipple size, there are certain cases where a faster flow nipple might be a more suitable option. For example, if you have a fast flow and your baby can nurse in 5-10 minutes, but is getting frustrated with bottles and taking 30-45 minutes to finish them. Assess your own flow and what will work for your baby. If everything is running smoothly, let it be.

What if I’m Exclusively Pumping?

Because breastmilk digests much quicker than formula and it is so easy to overfeed a baby when bottle feeding, experts still recommend using slow flow or “newborn” nipples even if you’re exclusively pumping. Just like any other breastfeeding mom, you will also want to feed your baby on demand (not according to a rigid schedule) and follow paced bottle feeding methods.

Typical nursing sessions last 15-20 minutes, so expect your feedings to take around that same amount of time. Be sure to allow your baby plenty of time to drink his/her bottle and don’t rush through a feeding as quickly as possible (source).

Other Considerations

Remember Note


If your baby seems unhappy with the current nipple size, but doesn’t respond positively to a faster flow nipple, there may be other factors to consider. You may want to try a different shape of nipple (such as an orthodontic or angled nipple), texture of nipple, length of nipple, or a different venting system.

The problem might also not be with the equipment itself either. Your baby may be going through a distracted phase, teething, having a medical issue, or not happy with the temperature of the milk. You could also have high lipase in your breastmilk or possibly misinterpreting your baby’s cues as a sign of hunger (source).

In Summary

Having the right size nipple will make feedings faster, easier, and much more enjoyable for everyone involved. Nipple size may depend on if your baby is formula fed or breastfed, their age, and other readiness cues.

Formula fed babies will typically move up in nipple size the older they get, but age isn’t necessarily always an indicator.

Watch out for other readiness signs, such as your baby sucking harder than normal, taking forever to finish a bottle, smacking at the bottle, and being hungry shortly after feeds she didn’t finish.

Most breastfed babies will never use anything other than a slow flow nipple, as it best resembles milk flow during nursing and also helps prevent overfeeding and keeps baby preferring the breast.

Bottle nipple size isn’t a one-size fits all kind of guide, so assess your situation and figure out what will work best for you and your baby. If everything is going smoothly with the current size nipple, then let it be.

When did you switch nipple sizes on your baby’s bottles? Tell us how you knew it was time to make the change in the comments below, and be sure to share this post with all of your bottle feeding friends.

2 Reader Comments

  1. My 5 week old has been on comfort milk with level 2 teat for 2 weeks due to bad colic. He’s now displaying all of the above signs so we’ve moved him to level 3 (Dr Brown’s) from today to see if that helps. He’s always been a very aggressive eater and flattened the level 1 teats from birth!!

  2. Heather

    What if a level 2 is too small and level 3 too fast ? She shows signs of both.

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