This guide has been written in collaboration with, Kirstin Linden, a certified lactation consultant, to ensure accurate and supportive information for your breastfeeding journey

Whether we’re talking jeans, bras, or dresses, finding the perfect fit is so satisfying. However, when it comes to breastfeeding, finding your fit is less about style and more about function (making it doubly important!). 

Find the best breast pump flange size for your boobs, and you’ll experience a boost in comfort and breast milk production. But just how do you find that perfect breast pump flange fit? Don’t worry — we’ve got you covered. 

What is a breast pump flange?

Let’s start with a little breast pump 101. A breast pump flange (or shield) is the part of your pump that fits directly over your breast. In other words, it’s super important that this piece is matched to your anatomy.

The breast flange covers your nipple and areola (that’s the ring of darker-colored skin surrounding the nipple). Its job? To form an airtight seal between your breast and the pump — your breast flange must form a firm vacuum around the breast. 

How do I know what size flange to use for my breast pump?

So, how do you find the perfect breast flange size? Well, first you’ll need to know the size of your nipple so that you can determine what size flange you’ll need. 

How to measure nipple size

Measuring your nipples is pretty straightforward, and you can do it in one of two ways:

• The easiest (and most accurate) way of sizing your nipples is to use Elvie’s handy nipple sizing guide, which you can download and print out for free.

• Alternatively, you can measure the diameter of the base of each nipple (the part where the nipple meets the areola) using a ruler and a debit or credit card. Line the card up with the edge of your nipple and place the ruler under the nipple to create a right angle. Take your measurement from the part where the base of your nipple is widest. 

It’s important to note that you shouldn’t measure your nipple directly after breastfeeding or pumping, as this may alter its natural size and give you inaccurate measurements.

Breast flange size guide

Generally speaking, choose a flange size that measures around 2-4mm more than the diameter of your nipple. This gives a little more room for flexibility. We’ve listed some of the most common sizes below.

Don’t worry if your exact nipple width isn’t listed above, just pick the closest appropriate size. Remember that your breasts are likely to change size and shape throughout your nursing journey too, so it’s always worth grabbing a few different sizes. At Elvie, we stock three different flange sizes — 21mm, 24mm, and 28mm.

Most manufacturers will list their sizes on their websites. You can find flanges for your Elvie pump on the Elvie Pump accessories page. 

How do I know I have the correct flange size?

Once you’ve got your breast pump flanges, it’s time to try them out. Generally speaking, you’ll know your flange sizing is spot on if:

• The flange feels comfortable — it should feel like a strong tug but no pinching pain

• Only your nipple and a small part (or none) of your areola enters the tunnel when you start pumping

• Your nipple has enough space to move freely inside the tunnel without rubbing up against it — this will prevent painful chafing, blisters or cracked nipples

• Once you’re finished pumping, your breasts feel soft and empty

• The amount of milk you’re able to express either stays the same as normal or improves

• Breast pumping feels comfortable and pain-free
  

However, you may need to consider a different flange size if:

• Your breasts still feel full after you’ve finished pumping

• Your nipple rubs against the sides of the flange tunnel, causing discomfort

• A large area of the areola is being pulled into the flange tunnel

• You notice redness at the base of the nipple either during or after pumping

• Your nipples or areola start to turn white during or after pumping

What if I pick the wrong flange size?

Getting that perfect fit isn’t just crucial for your comfort, it’ll also maximize your breast milk output. If your breast flange is too small, you could end up clogging your milk ducts. The vacuum seal won’t be tight enough if it's too large.

In either scenario, you’ll end up pumping out less of the good stuff and therefore decrease milk supply. Worse still, using the wrong flange size could cause pain and discomfort. In short, picking out a well-fitted breast flange is vital for you and your baby, so it’s worth taking the time to measure up!

What happens if a breast pump flange is too small?

A flange that is too small may cause excessive friction, pinching, or squeezing of the nipple. Your nipple or areola may become white or discolored, and you notice that you produce less milk and that expressing milk is painful.

What happens if a breast pump flange is too big?

When the flanges of your pump are too large, too much of the areola is pulled into the tunnel. This can cut off the milk ducts so they can’t properly express the milk.

How much areola should be in my breast pump flange?

Unfortunately, this isn’t an exact science. However, a general guideline is to aim for about 1/4 to 1/2 inch (6-12mm) of the areola to be inside the flange.

The nipple should be centered in the tunnel of the flange, and the flange should create a comfortable seal around the breast. It's important to use the correct flange size to ensure that the areola is not being pulled too far into the tunnel or that too much of the breast tissue is being pulled into the flange.

Can the wrong flange size affect milk output?

Yes, the wrong flange size can negatively affect the amount of milk you’re able to produce. A loose-fitting flange may not provide adequate suction — meaning milk may be left in the breast — while a flange that is too tight will constrict the breast and may lead to clogged milk ducts, which will mean a decrease in milk production. 

How often should I replace my breast pump flange?

Breast flanges should be replaced as needed, depending on how frequently they are used and how well they are maintained. If you notice any kind of discoloration, cracks, tears, or loss of suction, those are good signs that it’s time for a new flange. It's a good idea to have a spare set on hand, especially if you’re exclusively pumping or using a breast pump frequently. Exclusive pumpers may need to replace their flange more frequently, around every 6-12 months.

When it comes to your breast pump shield (or flange), size matters. Not only will ensuring you have the right size mean your pumping sessions will be comfortable and pain-free, but it’ll also help to maintain healthy and consistent milk production. Still unsure what size you need? Check out our nipple sizing tool to find out.