Because one size definitely doesn’t fit all..

I’ve helped so many mums with nipple pain when it comes to pumping, and you know what’s often the culprit? An ill-fitting breast pump flange. Unfortunately, the majority of mums who are using a pump do not have the right size, as most hospitals take an outdated “one size fits all” approach, with staff tending to size up when there is any discomfort.

If you’re using that standard 24mm shield that came with your pump, or someone’s told you to go bigger with a 28mm or 30mm, there’s a very good chance you’re using the wrong size. And that could be causing you unnecessary pain and affecting your milk supply.

Discussing the details of fitting a pump, and even what type of pump to use for each scenario is something I take my clients through during the pregnancy Breastfeeding Planning sessions and when I see them at home with their newborn.

Here’s what we actually know from research and experience

Recent research highlights that;

• Comfort and effective milk removal are highest when flange diameter closely matches nipple diameter plus room for movement (generally 1–2 mm). ¹
• Mismatched flange sizes can lead to reduced milk output and nipple trauma.²
• Ultrasound studies revealed that overly large or small flanges can cause edema, pain, and inefficient milk removal.³

When your nipple and areola are repeatedly suctioned too far into a plastic or silicone flange, it causes swelling, discomfort, redness, inflammation, and possibly trauma. We want to avoid this by measuring your nipple diameter properly and finding a flange that allows only your nipple to move during pumping – not your areola.

But it’s not just about comfort (though that’s important!). Flange fit directly impacts your milk yield, which matters hugely if you’re trying to increase or maintain your supply. When there’s trauma happening at your nipple, the pain and inflammation can block oxytocin – that crucial hormone that helps release your milk. Plus, swelling can physically narrow or block the milk flow, reducing your pumped volume.

Quick note: If your output is great and you’re comfortable, there is no need to read any further – Just keep this in mind if things change down the track.

How to tell if your flange is the RIGHT size

No pain or discomfort whilst pumping
Your breast feels ’emptied’ after pumping
Your milk volume is optimal or higher than with previous flanges

Signs your flange is TOO BIG

Your nipple swells up whilst expressing
Your breast loses contact with the flange during pumping
Milk leaks out the bottom of the flange
You are using a high vacuum to get any milk out
Your letdown (start of flow) takes several minutes
Your breasts still feel full after expressing / not fully drained
Feels ‘tight’ but there’s still room between nipple and flange sides

Signs your flange is TOO SMALL (less likely)

Your nipple doesn’t move freely at the start of pumping
Your nipple doesn’t fit into the flange or insert at all

Measuring your nipple for a flange

At the end of the day, the right flange size for you is the one that feels best, gives you the best output, and doesn’t pull any areola or breast tissue in – only your nipple.

How to measure properly

Choose a breast shield size that’s as close to your nipple diameter as possible. For example, if your nipple is 16mm wide, you’d likely need a 17mm breast shield.

Best practice: Try a few sizes around your measurement. Using that 16mm example, I’d suggest trying 15mm, 17mm, and 18mm shields to see which feels most comfortable.

Important: Always measure both nipples – it’s incredibly common to need different sizes for each breast.

If you have access to a printer, a nipple ruler is brilliant for finding your perfect fit or you can use something more tailored like the silicone measuring ruler above (more brands are starting to make these now which is positive to see!).

Things to remember

Your nipple size can change throughout your feeding and pumping journey, so it’s worth checking in with sizing if things start feeling off.

Other causes of pump pain: Sometimes discomfort isn’t about flange size – it could be that your nipple isn’t centred properly (stop and reposition), your vacuum is too strong (turn it down), or there’s a deeper cause like vasospasm, breast inflammation, or nipple infection / poor healing.

The bottom line? You shouldn’t have to suffer through painful pumping sessions. Getting the right flange size is often a simple fix that makes a world of difference to your comfort and milk supply.

If you’re still struggling with pump pain or low output after trying different sizes, it might be time to get some personalised support. Every pumping journey is different, and sometimes you need an expert eye to troubleshoot what’s really going on.

Need support with supply or troubleshooting your pump? If you have a Youha pump (use code JWPCARE for 10% off) I highly recommend their amazing customer support team. If you are wanting to work 1:1 with an experienced Lactation Consultant, please explore my services here or contact me here, I would love to support your feeding journey.

References

1. Kent, J. C., Ramsay, D. T., Doherty, D. A., Larsson, M., and Hartmann, P. E. 2008. “Response of Breasts to Different Stimulation Patterns of an Electric Breast Pump.” Journal of Human Lactation 24 (2): 168–78. https://doi.org/10.1177/0890334408316071. 
2. Prime, D. K., Geddes, D. T., Spatz, D. L., Robert, M., Trengove, N. J., and Hartmann, P. E. 2012. “Using Milk Flow Rate to Investigate Milk Ejection in the Left and Right Breasts during Simultaneous Breast Expression in Women.” International Breastfeeding Journal 7 (1): 1. https://doi.org/10.1186/1746-4358-7-1.
3. Geddes, D. T., Kent, J. C., Mitoulas, L. R., and Hartmann, P. E. 2008. “Tongue Movement and Intra-Oral Vacuum in Breastfeeding Infants.” Early Human Development 84 (7): 471–77.https://doi.org/10.1016/j.earlhumdev.2007.12.002.

As well as my own experience and knowledge around this aspect of supporting mums to breastfeed and feed their baby breastmilk, this article also draws inspiration from Cherished Parenting (Perth) and Nurturing the Flow (Melbourne)- two excellent sizing and pumping support businesses.