When I first started pumping, I assumed the flanges in the box would be fine. But I quickly learned there’s a big difference between a flange that technically fits and one that actually feels comfortable, protects your nipples, and helps you pump efficiently.
Getting the right flange size completely changed my pumping sessions. I'm talking less pain, less wasted milk, and more comfort.
This guide shares everything I wish I’d known sooner about flange sizes: how to measure properly, when it’s time to adjust, and how to choose the size that makes pumping easier and more effective for you, mumma.
What Is a Flange (or Breast Shield) and Why Does Size Matter?
A flange (sometimes called a breast shield) is the part of your breast pump that sits over your nipple and areola. It’s what creates the seal and gentle suction that draws milk out. But here’s the thing - if it doesn’t fit properly, your pumping sessions can feel uncomfortable and much less effective.
Too small: your nipple may rub or pinch, causing soreness and even blocked ducts.
Too large: too much of your areola gets pulled in, suction feels weak, and milk flow can slow right down.
So many mums don’t realise they’re using the wrong flange size[1], and it can make all the difference. Finding the right fit isn’t just about comfort, it’s about protecting your nipples, keeping milk flowing, and making each pumping session a little easier - and honestly, we’ll take easier any way we can
What are the Signs your Flange isn’t Right?
Here’s what I noticed in myself, and what many experts agree are red flags:
| Flange Too Small | Flange Too Large |
|---|---|
| Nipple pinches or burns; tip turns white | Suction feels weak; areola is pulled into the tunnel |
| Milk output is low even after long pumping | You have to turn up suction high to feel anything |
| Nipples are sore, cracked, or blistering | Lots of air sounds or leaks; little feedback from pump |
If you experience discomfort that's persistent, or your milk seems much less than it should be, adjusting flange size could be the missing piece[2].
How to Measure Your Flange Size (Step-by-Step)
Here’s how I measured mine (and tweaked until it felt just right):
1. Wait until after feeding or pumping (or at least once your nipple is rested). If you measure immediately after feeding, swelling can distort size.
2. Use a ruler or measuring tape with millimetres. Measure the diameter of your nipple alone - from tip to base - excluding the areola. Some guides say measure when your nipple is a little stimulated or erect to mimic what it looks like during pumping [3].
3. Once you have that measurement (e.g. 18 mm), add about 2–4 mm to allow space for movement and avoid rubbing.
4. Compare this to the flange sizes your pump offers. The New Beginnings Double Electric Breast Pump includes two flange sizes in the kit, which helps you try both ends. The Wearable Breast Pump may require trying flange inserts or additional sizes if needed.
5. Test with a short pumping session: start at low suction, check for comfort, check if nipples touch the walls of the tunnel, check milk flow.
How Your Flange Size May Change Over Time
One thing that really surprised me, even as a mumma now feeding my third bub, is that my flange size didn’t stay the same. I actually needed to adjust it a few times in those early months, and it made such a difference once I realised why.
- Nipples change size thanks to hormone shifts, engorgement, or fluctuations in milk supply.
- Tissue can swell or settle as you heal after birth or even just after feeding.
- Your pumping style matters - pumping frequently, or swapping between a hospital-grade pump and a wearable, can change how a flange fits.
So now I check every few weeks, or anytime I notice pain or less milk coming out. Having a couple of extra flange sizes (or inserts) ready at home means I don’t have to scramble when things change.
Quick Reference: Flange Size Table
Here’s a rough guide many parents use (not all pumps are the same, check with yours):
| Nipple Diameter | Suggested Flange Size |
|---|---|
| 15–16 mm | 18–20 mm |
| 17–18 mm | 20–22 mm |
| 19–20 mm | 22–24 mm |
| 21–22 mm | 24–26 mm |
| 23–25 mm | 27–30 mm |
Use this as a starting point, but always test.
A side comment on Wearable Pumps vs Double Electric Pumps
Using a wearable pump (like the New Beginnings Wearable Breast Pump) adds some extra considerations:
- Wearables move with your body (walking, bending etc.), so the seal needs to be very good to avoid leaks—so flange fit becomes even more critical.
- Wearables may use silicone inserts to customise the tunnel. If your pump includes inserts or options, try different sizes/inserts.
- Because wearable flanges often have less rigid back support or structure, comfortable fit and centre alignment are especially important.
With double electric pumps, since the pump is stationary (you often sit still), minor misfits might be less noticeable, but over time they still cause fatigue or damage if not corrected.
How New Beginnings Pumps Handle Flange Sizes
Here’s how NB’s pumps make life easier (from what I’ve used):
- Double Electric Breast Pump: Comes with two flange sizes in the kit, which allows immediate trial between sizes. If one feels off, you can swap to the other. You can also purchase extra sizes or add ons here.
- Wearable Breast Pump: The standard 24mm flange is included, plus two 21mm flanges and two 19mm flanges for a customised fit. To make things even easier, each box also comes with a nipple ruler to help you measure accurately.
Tips & Tricks from My Pumping Journey
- Start with the larger flange if you’re between sizes, because too tight = pain.
- Always centre your nipple in the tunnel before turning on suction.
- Use low suction + ramp up; high suction from the get go just amplifies discomfort.
- Keep extra flanges or inserts clean and dry - rotating helps ease pressure.
- Replace flanges when you see wear: cracks, deformation, or discolouration. Damaged parts affect the seal.
Getting the right flange size isn’t glamorous. It’s not cute or fun. But it is one of those small tweaks that changes everything: less pain, better milk flow, more confidence when you pump on the go, or need to rely on your wearable pump during a busy day.
You’re already doing so much. Getting the flange fit right is just one of the ways to give your body ease. You deserve that comfort.
Relevant Articles
- For what to expect in a realistic pumping day, check out A Realistic Day in the Life of Pumping.
- If you’re feeling discomfort, What Should I Do If Breastfeeding Is Painful has great tips.
Flange FAQ Section
What if the flange I need isn’t included with my pump?
You can often buy additional flange sizes or use inserts (silicone) compatible with many pumps. NB double electric pump comes with two sizes.
How often should I re-measure?
Every few weeks in the early postpartum period, or whenever you notice discomfort, reduced milk output, or when your body feels different (engorged, swollen etc.).
Does flange size affect milk supply?
Yes: a well-fitted flange helps express milk more fully and efficiently. A wrong fit can reduce output and make pumping longer and more exhausting.
Can I mix flange types (plastic vs silicone)?
Yes, some materials are gentler (silicone) and can reduce friction. Some wearable pumps use softer materials. Just ensure the fit and seal are good.
Is discomfort ever normal?
A little sensitivity when you first start is common. But persistent pain, soreness, or damage is not something you should just endure. Adjust flange, check suction settings, or consult a lactation consultant.
How do I know if my flange size dropped my milk output?
You might notice longer pumping sessions with little milk, or feeling exhausted despite time spent. If flow seems weak, check your flange size and suction settings.
Can I use the same flange size for both breasts?
Sometimes - you may find one breast’s nipple is slightly different size from the other. If fit is off on one side, using different flange sizes per side can help.
When should I upgrade to a larger or smaller flange insert/sizes?
If you feel rubbing or pain → flange too small. If suction feels weak or areola is pulled in → too large. Also if your measurement changed (post-birth, during engorgement, etc.).
