Breast Pump Flange Sizes Explained (and the Mistake I Made)
“Who gives an F about flanges?” – Me, probably, 8 years ago.
Wrong. So wrong.
When I was pumping for my kids, I used the 24mm flanges that came standard in the box. Both times. No questions asked. I had a little oversupply, so I figured I was fine and never bothered to experiment with other sizes.
Big mistake.
My Flange Fit Wake-Up Call
Here’s the deal: I have small nipples. My non-lactating size is around 10mm. Yes, nipples change and grow during pregnancy and breastfeeding, but there was no chance mine doubled in size. I should have been using a much smaller flange all along.
Now, do I know for certain what would have been different if I’d sized down? No. But I do know this:
I might have pumped more efficiently.
I might have avoided clogs and discomfort (especially on those work trips with constant pumping).
I would have saved myself a lot of second-guessing.
And that’s why I’m sharing this — so maybe another mom doesn’t repeat my “just use what’s in the box” mistake.
Why Flange Fit Is So Important
Flange size is not one-size-fits-all. (If only, right?) Using the wrong size can lead to:
Pain and nipple trauma (ouch).
Clogs or mastitis risk from ineffective milk removal.
Decreased output: your body only gives what your pump asks for, and the wrong flange can “ask” incorrectly.
Getting measured—or at least experimenting with different sizes—can make a huge difference in both comfort and supply.
The Wide World of Nipples and Flanges
Here’s what a lot of pumping parents don’t realize:
Many parents fall in the 16–20mm range.
Some need much larger sizes — 28mm and up. Totally normal, as long as they are the right size for you.
Nipples on the same body can even be different sizes. (Sisters, not twins!)
The bottom line? Your nipples are unique, and they deserve flanges that fit them.
How to Find the Right Flange Fit for You
So, how do you know which flange size is right? Here are some steps to guide you:
Measure your nipple at the base (not including the areola) using a soft measuring tape, nipple ruler, or even printable sizing guides many pump companies provide. Do this before pumping for the most accurate measurement.
Add 1–3mm to your nipple diameter to determine your starting flange size. For example, if your nipple measures 15mm, you might start with a 17–18mm flange.
Test it out. When you pump, your nipple should move freely in the tunnel without rubbing or pulling in excess areola. If it’s uncomfortable, pinchy, or your output drops, try another size.
Remember your body changes. Nipples can fluctuate in size throughout your pumping journey, so what works at 6 weeks may not work at 6 months. Don’t be afraid to reassess.
When in doubt, ask for help. A lactation consultant (IBCLC) can measure and fit you to help take out the guesswork.
So, were you more informed than me? Or did you also rock the straight-outta-the-box 24s without a second thought? (Be honest, this is a safe space.)
