How to choose the right size flange for your breast pump
- Molly Veltz
- Mar 12
- 5 min read
Updated: Nov 3
I'm a Lactation Consultant, but I'll be honest, I don't know your ideal flange size. Flanges, which are plastic or silicone funnels that fit over your breasts, can be ill-fitting and uncomfortable. They contain a tunnel portion that draws your nipples inside to trigger a release of milk. When they don't fit correctly, they don't empty your breasts well, and that impacts your milk supply.
Many moms who are planning to breastfeed imagine their newborn baby bringing in their milk supply by nursing frequently in the early days and weeks. This is the best case scenario! The breast pump shows up a few weeks later, when supply is already established, and begins to remove and collect some extra milk that can build a freezer stash for a return to work, or relief bottles. Once back to work, mom uses the pump every 3 hours to remove milk while away from her nursing baby. However, for some moms, the pump comes onto the scene immediately, for example, after the birth of a premature baby. Even full-term babies who are going to breast, sometimes aren't getting quite enough milk at the breastaurant, so we need to add pumping to the equation right away. And with the pump, come an array of options for flanges.
When your lactation consultant arrives, she can measure your nipples. Providing this service is relatively new. When I became an IBCLC in 2010 and began working on the maternity floor of a large medical center, we provided most moms with a standard size 24mm flange, which was included in our pump kits that accompanied our hospital grade Medela pumps. When we switched to Ameda pumps, the standard size was 25mm. These seemed to work for most moms, but based on visual assessments and reported levels of comfort, often we would size larger, to a 28 or 30. We even had size 36mm, which we occasionally used. The manufacturer instructions from Medela and Ameda back then, were the same as they are today: measure the diameter of the base of the nipple, and add 2-4 mm to find the best size. Instructions from Spectra are identical. All three companies warn against having one's nipples rubbing on the sides of the tunnel, stating that nipples should move freely in the tunnel for the best fit.
Fast forward to 2025. There is a growing movement to adopt much smaller flanges that do not allow any extra "room" for the nipple. The result is that the sides of ones' nipples will make contact with the tunnel. However, when a nipple is stuffed tightly into the flange tunnel, it can impede the nipple from being stretched. The stretching is what triggers hormones to release milk! This newer method results in exactly what we previously tried to avoid. However, the movement to size smaller has gained popularity and I have seen this growing trend work for many moms.
Choose your Camp! Tried and True, VS. New & Improved?
How confusing is that? There are two recommendations that directly contradict one another! When you pull out your commercial pump and read the instructions, it'll steer you to measure in the traditional way: measure the base of your nipple where it meets the areola, and then add a few millimeters so that your nipple has space and can move freely in the tunnel. The disadvantage of this method is that in some cases, all that room leads to your nipples and areolas becoming swollen. With the newer approach, you'll be sizing down to the smallest diameter of your nipple shaft, which is sometimes cone-shaped, ensuring that only your nipples enter the tunnels of the flanges, without even a tiny perimeter of areola. That's going to be a very snug fit, but advocates for this method claim that it avoids swelling, is more comfortable, and can increase yield.
What does the research tell us? It's no surprise that there is a limited amount of literature on this subject which concerns the comfort of women. One recent study that compared traditional and newer sizing methods, was released in the fall of 2024. It was a small study, but 60% of the participants who already had a full supply, preferred the more snug fit. Another data set of 2,000 lactating people, found that 75% of them had ultimately chosen a flange that was 0-2 mm larger than their nipple base diameter. We lactation consultants anxiously await more research in this area!
In the meantime, word has spread that a poorly fitting flange can sabotage milk supply, and now every breastfeeding mom I encounter in the hospital, asks for a nipple measurement. I'm happy to use my circle tool or calipers to obtain nipple measurements. But consider this confounding fact: Nipples can change shape and size during the early days of breastfeeding, due to swelling from IV fluids, your baby’s latch, or engorgement. Therefore, this initial measurement is nothing more than a starting point. And with each child, your nipples may become more elastic, so you don't want to assume that the best size flange is the one you used with your last baby.
Word to the Wise:
No matter which camp you subscribe to, it will involve some experimentation. During the selection process, always ensure the following:
Measure your nipples before a pumping or nursing session, not after.
Pumping should not hurt, and you may increase your pump suction as high as you can comfortably tolerate it. It helps to lubricate your nipples or the pump flange with coconut oil prior to pumping.
Whether your nipple is moving freely in the flange or rubbing on the sides, your nipple has to be stretched in order to trigger a let-down of milk. Make sure the fit isn't so tight that it prevents that critical stretch!
If your nipples are becoming sore or you have skin breakdown on the sides, you may want to size larger.
If swelling is very noticeable and causing discomfort, you may want to size smaller.
Many moms use different sizes on each breast, since our anatomy is rarely perfectly symmetrical.
Breast pumps are just starting to include smaller flanges, in addition to the standard 24/25mm. If you want to try the smaller fit, you may need to special order an insert.
Consider your comfort and yield first and foremost!
If the shoe fits...
How many times have you ended up with a comfortable shoe that's a half or full size different than the size you thought you were? Likewise, trial and error leads you to the flange that feels comfiest and empties your breast best. Admittedly, sampling different sizes of flanges is not nearly as much fun as trying on a bunch of shoes! You may feel like Goldilocks during this process of elimination: too small, too big, too hard, too soft, too hot, too cold, and finally, maybe a middle ground that feels just right! Luckily there are some inexpensive kits that contain multiple sizes.
With all that said, here is a graphic that helps highlight the different types of fits, as well as a good illustration of the nipple vs the areola. You'll notice that this graphic claims there is only one "right" fit, but that is actually left up to interpretation! However, I think it's fairly sensible, as a starting point, to aim for your flange to resemble the picture at the bottom right. If you are uncomfortable or not getting good output, you could try a bit larger or a bit smaller from there.
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