For a newborn, you want a slow-flow nipple, typically labeled “Level 1,” “Newborn,” or “Slow Flow” depending on the brand. Premature or very small babies may do better with a “Preemie” or “Level 0” nipple, which delivers milk even more slowly. The right size isn’t really about your baby’s age, though. It’s about how well they handle the flow of milk during a feeding.
How Nipple Sizing Works
Bottle nipples are sized by flow rate, not by physical dimensions. A lower number means milk comes out more slowly. Most brands use a numbered system that looks something like this:
- Preemie or Level 0: Slowest flow, designed for premature infants or babies who need extra time to coordinate sucking and swallowing
- Level 1 or Slow Flow: Standard starting point for full-term newborns, typically labeled for 0 to 3 months
- Level 2: Faster flow, generally suggested for 3 months and older
- Level 3 and beyond: Progressively faster, for older babies who feed more efficiently
That said, every baby has unique feeding skills that don’t always match their age or size. A three-month-old might still do best on a Level 1, while another baby the same age is ready for Level 2. The label on the package is a starting point, not a rule.
Labels Can Be Misleading
One important thing to know: the words on the packaging don’t tell you much about the actual flow rate. A study published through the National Institutes of Health tested nipples from more than a dozen major brands, all labeled “Slow,” “Newborn,” or “0 to 3 months.” The actual flow rates ranged from 1.68 mL per minute on the low end to 15.12 mL per minute on the high end. That’s nearly a ninefold difference between two nipples that both claim to be for newborns.
Even within the same brand, two nipples carrying the same “Newborn Flow” label produced significantly different flow rates. So if you switch brands and your baby suddenly seems to struggle or gulp, the nipple may be delivering milk much faster (or slower) than what they’re used to, even though the label looks the same.
Signs the Flow Is Too Fast
When milk comes out too quickly, your baby can’t keep up. You’ll notice coughing, sputtering, or choking during feeds. Milk may leak from the corners of their mouth. They might pull away from the bottle frequently, arch their back, or seem stressed while eating. If you’re seeing these signs, try a slower nipple. Babies who regularly deal with too-fast flow can start refusing the bottle altogether or swallow excess air, which leads to more gas and spit-up.
Signs the Flow Is Too Slow
A nipple that’s too slow forces your baby to work harder than necessary. According to Nationwide Children’s Hospital, the key signs include feedings that drag on unusually long, fast sucking with very few swallows, the nipple collapsing inward from suction, and general fussiness or frustration during the feed. Seattle Children’s Hospital notes that a typical bottle feeding shouldn’t take more than 20 minutes. If it consistently does, check whether the nipple is clogged or if your baby has outgrown the flow rate. A clean nipple turned upside down should drip at about one drop per second.
Choosing a Nipple for Breastfed Babies
If you’re breastfeeding and supplementing with a bottle, staying on a slow-flow nipple longer is generally a good idea. Breastfeeding requires more active effort from your baby than most bottles do. When a bottle delivers milk too easily, some babies start to prefer the bottle because it’s less work. Sticking with a Level 1 or even a Preemie-flow nipple keeps the effort level closer to what your baby experiences at the breast, making it easier to switch back and forth. Dr. Brown’s Medical guidelines specifically recommend their Preemie Flow nipple for newborns who are breastfed and receiving supplemental bottle feedings.
When to Move Up a Size
There’s no set schedule for sizing up. Instead, watch your baby’s behavior. If feedings are taking noticeably longer than they used to, your baby seems frustrated or impatient at the bottle, or they’re sucking hard without getting much milk, it’s worth trying the next level. Move up one size at a time and observe. If the faster nipple causes coughing or gulping, go back to the previous one and try again in a couple of weeks.
Some babies stay on Level 1 for most of their first year, especially if they’re also breastfeeding. Others move to Level 2 around three or four months. Let your baby’s cues guide you rather than the age ranges printed on the box.
When to Replace a Nipple
Even the right size nipple needs to be swapped out regularly. Most manufacturers recommend checking nipples for wear after about three months of use, though they can break down faster depending on how often you use and sterilize them. Look for discoloration, a sticky or tacky texture, cracks in the silicone, or small pieces flaking off. Any of these means it’s time for a new one.
A less obvious sign is a change in flow rate. A worn nipple may let milk through faster than it did when new. You can test this by filling one bottle with the old nipple and another with a fresh one, turning both upside down, and comparing how quickly they drip. If the old one is noticeably faster, replace it.