Bottle Nipple Sizes: How to Tell if the Flow Is Too Fast or Too Slow

Flow levels aren't standard

• Nipples are sold as preemie or extra-slow, slow (often "level 1" or "newborn"), medium, and fast, sometimes numbered 1 to 4 or more.
• There is no industry standard. One maker's slow nipple can flow faster than another's medium, and even nipples in the same pack can differ.
• The age on the package is a marketing guess. Go by how your baby feeds, not by their age. Many babies stay on a slow nipple for months, and that's fine.
• Breastfed babies who also take bottles usually do best on the slowest flow they can feed comfortably with, alongside paced feeding. See the combination feeding guide.

Signs the flow is too fast

• Gulping, coughing, sputtering or choking.
• Milk leaking out of the corners of the mouth.
• Clicking sounds or a loose seal; wide, worried eyes; pulling off often.
• Finishing a full bottle in under 5-10 minutes, then spitting up a lot, gassiness or hiccups.
• Later preferring the bottle and fussing at the breast.

Signs the flow is too slow

• Frustration: sucking hard, then pulling off and crying.
• The nipple collapses or flattens while sucking (also check that the vent or collar isn't too tight).
• Feeds regularly stretching past 25-30 minutes.
• Falling asleep before finishing and waking hungry soon after.
• Note that a tired, sleepy or unwell baby may also feed slowly, so look at the whole picture.

How to test a nipple

• Turn a filled bottle upside down without shaking. Milk should drip steadily, roughly a drop per second, not pour in a stream.
• Watch a feed: aim for a calm rhythm of a few sucks, a swallow and a breath, over about 10-20 minutes.
• Try one change at a time for a couple of days before judging.
• Never cut or enlarge a nipple hole to speed things up or to get cereal through. It can cause choking, and cereal in a bottle isn't recommended unless the doctor prescribes it.

When to replace nipples

• Check every nipple before each use: pull on it and look in good light.
• Replace right away if cracked, torn, thinning, sticky, swollen, discolored, or if the hole looks bigger. A torn piece can be a choking hazard.
• Many makers suggest replacing every 2-3 months even if it looks fine. Teething babies chew through them faster.

Choosing bottles

• Standard narrow, wide-neck and angled bottles all work. A wide-based nipple doesn't automatically mimic the breast; how the baby latches and the flow matter more.
• Glass, plastic and stainless steel are all options. Baby bottles sold in the US are made without BPA. Check the label before putting plastic parts in a dishwasher or steam sanitizer, and never warm milk in a microwave.
• Anti-colic vents and valves may reduce air swallowing for some babies, but evidence that any bottle prevents colic is limited. Good positioning, paced feeding and burping matter more.
• Buy one or two to start. If a baby refuses one style, try another before buying a whole set.

Check in with the pediatrician or an IBCLC if

• Choking, coughing or color change with feeds continues even on the slowest flow. This can be a sign of a swallowing problem and needs a check. Call 911 for blue lips or pauses in breathing.
• Feeds always take over 30 minutes, or weight gain is slow.
• The baby clicks, loses milk or can't keep a seal on any nipple, which can point to tongue tie or oral motor issues (see the breastfeeding problems guide).