Switching Baby Bottle Nipple Sizes: Knowing When The Time Is Right

Is your baby getting frustrated with the bottle and you’re wondering whether to go up a nipple size? How do you know when it’s time to make the change? Were you even aware there were different nipple sizes and that it could make a difference?

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 more comfortable and enjoyable for everyone involved. But how do you know which is the right size nipple for your baby and when to move up a size?

Let’s 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 with the bottle.

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    When To Switch Bottle Nipple Sizes

    The nipple size for your baby’s bottles will depend on if they are formula fed or breastfed, their age, and other readiness cues. Nipple size is essentially the flow rate – how fast your baby can get liquid will depend on the labeled nipple size.

    For A Formula Fed Baby

    For formula fed babies, an age guide for nipple sizes (flow) usually comes 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.

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    The faster nipples are meant for older babies, because they eat more at each feeding and can handle the flow of milk better. 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 the best determinant of nipple size, as all babies are different. There are other signs besides age to indicate when 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 a long time to feed (30 min. to 1 hour).
    • Eating less at feedings, but getting hungry again soon after.

    If your baby isn’t showing any signs of frustration or taking forever to eat, there is no need to move up a size. But if your baby is showing some of these signs, 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 corner of their mouth, 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 their 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 easy to inadvertently 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, in certain cases a faster flow nipple might be a more suitable option. For example, if you have a fast flow and your baby can nurse in five to ten minutes, they may get frustrated with bottles that take 30-45 minutes to finish.

    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 breast milk digests more quickly 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, 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. Allow your baby plenty of time to drink their bottle and don’t rush through a feeding (source).

    Other Considerations

    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 (such as an orthodontic or angled nipple), texture, length of nipple, or a different venting system.

    Keep in mind a ‘preemie nipple’ doesn’t necessarily mean it’s slow flow, though for some brands they do. And some brands don’t go by age, but rather label the nipples ‘level 1’ and level 2.’ You’ll need to read the packaging or even check the manufacturers website to get a feel for what these labels mean.
    Headshot of Michelle Roth, BA, IBCLC

    Editor's Note:

    Michelle Roth, BA, IBCLC

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


    Keep The Size Right

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

    Bottle nipple size isn’t a one-size fit 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.

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