Breast Pump Flange Fit Guide: How to Find the Right Size

Choosing the right pump, learning its ins and outs and figuring out how to safely store your milk are things you’ve likely thought through if you’re pumping breast milk for your baby. But there’s something that many pumpers don’t give much thought to at all: flange size.

Also called a breast shield, the flange is the part of your pump that sits around your areola and nipple and cups your breast while you’re pumping. Using the proper size is key to an efficient and comfortable pumping session. But it’s not always obvious to check for a correct fit—and many pumpers are using the wrong size flange without even realizing it.

Here’s what you need to know about finding the right size breast pump flange: why it’s important, how to measure (and the tools you’ll need to do it) and how to be sure you’ve got the proper fit.

What Is a Flange?

A flange, also called a breast shield, is an important part of any breast pump. Shaped like a funnel, the flange goes around the nipple and areola and surrounds the breast during pumping. Flanges are most commonly made from plastic or silicone and come in various sizes. Some pumps come with multiple flanges in different sizes, while other pumps require you to purchase them separately.

Plastic versus silicone flanges

The type of flange you choose is a matter of personal preference. Many pumpers find silicone flanges more comfortable than traditional plastic ones, but not all. If you’re a frequent or exclusive pumper, you may want to consider giving silicone a try as they are soft, moldable and tend to create less friction as compared to plastic flanges. But many pumping people do just fine with (or even prefer) plastic options.

Why Does Flange Size Matter?

There are many reasons why pumping with a properly sized flange is important, but two rise to the top according to Rebekah Kimminau, International Board Certified Lactation Consultant (IBCLC) and owner of The Baby Gear Consultant: comfort and efficiency.

“Pumping with a properly sized flange will reduce any nipple damage and pain. You’ll also see the best output and be most likely to empty your breasts at each pumping session,” she explains. Both of these factors are a pretty big deal, especially if you’re someone who pumps exclusively or even regularly. “No one wants to be in pain while pumping, and being in pain can actually cause a decrease in milk supply. And when you empty your breast, your body gets the signal to continue making milk, which allows you to continue the positive cycle of milk-making.”

All flange sizes within the US and Canada are standard and use measurements in millimeters (mm), according to Kimminau. Some companies may size their flanges in small/medium/large, but will also correlate the size with a millimeter measurement. Most pumps come with two standard sizes, a 24-millimeter flange set and a 27-millimeter one.

Whether you’re exclusively pumping or only pumping occasionally, flanges can wear down over time. You may be able to get flanges and other breast pump-related parts free (depending on your insurance coverage) through Babylist Health—so be sure to check!

How to Measure Flange Size

Many pumpers assume that the size of your flange should correlate with the size of your breast—but that’s actually not the case. More important than breast size is the size of your nipples and your areolas, Kimminau points out. “Many people with large breasts have small nipples and will need a small flange, while many people with smaller breasts may have larger nipples and need larger flanges,” she explains. That’s why measuring your nipples is such an important step when you’re trying to figure out the best flange size for you. Follow these three steps.

1. Learn where to measure.

Before you jump into measuring, you’ll need to know what you’re measuring. To find the correct flange size, you want to focus on your nipple, not your areola.

2. Measure your nipple size.

Next, you’ll need to measure the size of your nipples. One easy way to do this is by using Babylist’s Breast Pump Flange Sizing Guide. Print the sizing guide at 100 percent scale and follow the directions for using the ruler. Be sure to measure your nipples prior to pumping and gently stimulate them before you begin. You’ll also need to measure both nipples, as they may be different sizes.

To find your flange size, take this measurement (the diameter of your nipple) and add two to three millimeters, then round up to the nearest flange size. So, for example, if you measure your nipple at 21 millimeters, your flange size would be 24 millimeters.

You can also refer to this flange size chart:

Don’t have access to a printer or simply don’t want to deal with printing and cutting? You can use a special nipple measurement tool, like this nipple ruler that Kimminau recommends. You can also use a standard ruler or measuring tape; just know it can be trickier to get an accurate measurement this way since you’re dealing in fairly tiny units of measure. Be sure to measure your nipple from base to top and don’t include your areola. (Quick math: One centimeter equals 10 millimeters.)

3. Confirm the correct fit.

Once you’ve selected the correct size, you need to check for a proper flange fit. The flange should fit over your nipple. When the pump is on, it’s okay if a small amount of areola is pulled into the flange as long as your nipple fits well and you don’t experience any pain. Your nipple should not rub against the sides of the pump (that would mean the flange is too small), but you shouldn’t see too much of your areola getting pulled into the tunnel of the flange, either (which would mean your flange is too big).

Remember, it can take a bit of trial and error to find the proper flange size. If you’re noticing things like friction, pain, swelling, pinching or decreased milk supply, those are likely signals that you’re using the wrong size flange. Don’t be afraid to try a few different sizes and possibly even test out both plastic and silicone flanges. And always reach out to a lactation consultant with any questions or ongoing issues.