Measure your nipple diameter
Measure only the nipple diameter in millimetres, without including the areola. A simple ruler or nipple measuring guide can help give you a starting point for choosing the right flange size.
Breast Pump Guides
Breast Pump Flange Size Chart: How to Measure & Find Your Right Size
Finding the right flange size is one of the most important — yet often overlooked — parts of comfortable and effective pumping. If your flange doesn’t fit properly, it can affect everything from milk flow to comfort, even if you’re using a high-quality breast pump.
This guide explains how flange sizing works, how to measure correctly, and how to find a fit that works for your daily routine. If you’re using a wearable pump, getting the right fit becomes even more important. You can explore our guide on what makes a wearable breast pump comfortable, quiet, and easy to use every day — it covers what to actually look for before you buy.
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Why Flange Size Matters
A breast pump flange is the cone-shaped shield that fits over the nipple during pumping. Its job is to create a secure seal so suction can work effectively. When the flange size is right, pumping usually feels more comfortable and efficient. When the size is off, it may cause rubbing, pinching, pressure on the surrounding tissue, or reduced milk output.
Getting the size wrong can also have more serious consequences over time — including clogged milk ducts, mastitis, nipple damage, and a gradual reduction in milk supply. These are among the most common pumping complaints, and an ill-fitting flange is often the underlying cause. The Australian Breastfeeding Association provides free support and guidance for mums experiencing breastfeeding difficulties.
Because breast shape and nipple size can vary between mums — and can even change during your breastfeeding journey — flange fit is something worth checking regularly rather than assuming one standard size will always work.
It’s also common for each side to be a slightly different size, so measuring both nipples can help improve overall comfort and fit.
How to Measure and Check Fit
Measure your nipple diameter at the base in millimetres — do not include the areola. A ruler works best. Check in the mirror and measure after a feeding or pumping session when your nipple is relaxed. Once you have your measurement, add 2–4 mm to get your starting flange size.
No ruler? An Australian 5-cent coin is approximately 19 mm across and a 10-cent coin is approximately 24 mm — useful as a quick reference.
Important: Nipples expand slightly under suction while pumping. If your calculated size still feels tight during a session, try sizing up by 1–2 mm.
Flange Size Chart
| Nipple diameter | Starting flange size |
|---|---|
| 11–13 mm | 13–15 mm |
| 14–16 mm | 16–19 mm |
| 17–19 mm | 19–22 mm |
| 20–22 mm | 22–25 mm |
| 23–25 mm | 25–27 mm |
| 26–28 mm | 28–30 mm |
| 29 mm+ | 30 mm+ |
Add 2–4 mm as a starting point
Once you have your nipple measurement, adding around 2–4 mm gives a general starting point for flange sizing. Comfort and response during pumping should still guide your final choice.
Check how it feels during pumping
Your nipple should move freely inside the tunnel without rubbing, pinching, or pulling too much surrounding tissue. Only a small amount of areola should be drawn in. A correct fit should feel smooth and comfortable, while also supporting consistent milk flow.
Nipple shape can vary between individuals — including flat, protruding, or slightly inverted shapes — which means fit should always be judged by comfort and movement, not measurement alone.
Watch the guide
How to Check Your Breast Pump Flange Size — in 30 Seconds
A quick visual guide to measuring at the nipple base, spotting a poor fit, and checking that your FlowEase™ flange size is correct.
What this video shows
00:05How to measure your nipple size
00:10Signs your flange is too large
00:15Signs your flange is too small
00:20What a correct flange fit looks like
00:24BabyNera FlowEase™ flange inserts and sizing ruler
Signs your flange size may be too small
If your flange is too small, your nipple may not move freely during pumping. Common signs include:
- Rubbing or friction against the tunnel walls
- Pain, pinching, or burning during sessions
- Nipple appearing white, blanched, or discoloured after pumping
- Milk flow that feels restricted despite adequate suction
- Cracking, blistering, or soreness over time
Left uncorrected, a consistently too-small flange can contribute to clogged milk ducts and mastitis — a painful breast infection that may require medical treatment.
A too-small flange can produce a similar sensation to ghost pumping — where the pump feels like it's working but very little milk comes out. If this persists even after correcting your flange size, our guide on why your pump feels like it's working but no milk comes out can help identify what else may be happening.
Signs your flange size may be too large
A flange that is too large reduces suction efficiency and causes its own problems. Common signs include:
- Excess areola being pulled into the tunnel
- Suction feeling weak or unfocused
- A tugging or stretching sensation around the areola
- Reduced milk output per session
- Incomplete breast emptying over time
Consistently incomplete emptying can signal the body to reduce milk supply over time, making proper flange fit important not just for comfort but for maintaining production. If you're already noticing a drop in supply, our guide on what actually works to increase milk supply when pumping covers practical steps that can help.
Does flange size affect milk output?
Flange size can influence how effectively milk is expressed. A better fit supports more stable suction and positioning, which may help create a more consistent pumping experience over time. While every mum responds differently, many find that improving flange fit helps both comfort and efficiency.
What a good fit should feel like
With the right fit, pumping should feel comfortable and smooth. Your nipple should move freely, minimal areola should be pulled in, and the experience should not feel sharp, pinching, or overly tight. If something feels off, even a small size change can make a big difference.
When to Check Your Flange Size Again
Flange sizing isn't always a one-time decision. Your nipple size and breast tissue can change throughout your breastfeeding journey, and a size that felt right at first may no longer be the best fit later on. Consider rechecking your size if:
- You're in the early weeks postpartum, when swelling and engorgement are still settling
- Pumping starts feeling less comfortable than it used to
- Your milk output drops without another obvious cause
- You've had a significant change in body weight
- You switch to a different pump brand or model
Different pump brands also use slightly different flange designs, so a size that works well with one pump may not translate exactly to the same number with another.
Elastic Nipples and Why Standard Sizing May Not Work
Elastic nipples are nipples that stretch significantly under suction during pumping. Unlike non-elastic nipples, they expand to fill the entire tunnel — which can make measurement-based sizing unreliable. You might use the correct size by measurement and still experience poor output, discomfort, or tissue compression.
Signs your nipple may be elastic:
- Nipple fills the entire tunnel during pumping with no visible space around it
- Nipple appears white, pale, or compressed after pumping
- Output feels lower than expected despite using a correctly sized flange
- Trying a larger size doesn't improve comfort — it just allows more tissue to be pulled in
If you suspect elastic nipples, the approach is often counterintuitive: try a smaller flange size rather than larger. Pumping at a lower suction setting and using a silicone insert (see below) can also help create a more stable fit. A lactation consultant experienced in flange fitting can assess this in person if you're unsure — you can find an accredited IBCLC through Lactation Consultants of Australia and New Zealand (LCANZ).
Silicone Flange Inserts: A Simple Way to Fine-Tune Your Fit
Silicone flange inserts — sometimes called flange cushions or silicone shields — sit inside a standard 24mm or larger flange to reduce the effective tunnel opening to a smaller size. They're worth considering if:
- The flanges included with your pump are too large for your nipple size
- Your pump brand doesn't offer smaller replacement sizes locally
- You want a softer feel against the breast — inserts are noticeably more comfortable than hard plastic for many mums
Inserts are typically available in sizes from 13mm to 21mm and are designed to fit inside standard 24mm flanges. They work with most pump brands, including wearable pumps like the BabyNera FlowEase™ hands-free wearable breast pump.
A few things to know before buying:
- The size printed on the insert refers to the nipple tunnel opening, not the outer diameter
- They need to be washed after every session like any other pump part
- They can be a more affordable option than sourcing a full replacement flange set, especially for less common sizes
Tips for a More Comfortable Pumping Experience
Small adjustments can make a noticeable difference, especially if you use a wearable breast pump regularly as part of your daily routine.
Recheck fit if pumping feels uncomfortable
If pumping feels painful, tight, or inconsistent, flange size is one of the first things worth checking. Comfort should improve, not get worse, as you continue pumping.
Focus on comfort, not just measurement
Your measurement is a helpful starting point, but comfort and pumping response matter just as much. The best fit is one that feels natural and works well in practice.
A well-designed pump also matters
Flange size works together with the pump itself. Stable suction, comfortable positioning, and easy daily use all contribute to a better pumping experience.
Small changes can make daily pumping easier
Even a small fit adjustment can help make pumping more manageable, especially for mums trying to stay consistent across home, work, and on-the-go routines. Keeping your pump clean also plays a big role in making daily use easier and more comfortable. For a step-by-step routine you can follow after every session, read our guide on how to clean your wearable breast pump properly after every session.
Getting the Right Flange Is Only Half the Story
Once your fit is sorted, the next step is making sure you're using a pump that works with your body — not against it.
The BabyNera FlowEase™ wearable breast pump comes with six flange sizes — five inserts (16mm, 18mm, 20mm, 22mm, 24mm) plus the built-in 27mm flange — so you can find your correct fit from day one without buying inserts separately. That's a genuine advantage over most pumps that ship with only one or two sizes.
If you want to understand what separates a great wearable pump from an average one — suction, comfort, battery, and everyday fit — our complete wearable breast pump guide for Australian mums covers everything in detail.
Flange Size FAQs
These are some of the most common questions mums ask when trying to find a more comfortable and effective flange fit.
How do I know if my flange size is wrong?
Your nipple should move freely in the tunnel — if it rubs the walls, the flange is too small; if excess areola is being pulled in, it's too large. Other signs include pain during sessions, a white or blanched nipple after pumping, and unexplained drops in output. Remeasure and try a different size before assuming a supply issue.
Should my nipple touch the sides of the flange tunnel?
No — your nipple needs space to move freely with the suction cycle. A small gap around the nipple is correct. Rubbing against the tunnel walls means too small; excess areola being pulled in means too large.
Can the wrong flange size affect milk output?
Yes — significantly. A too-small flange compresses the nipple and restricts milk ducts; a too-large one disperses suction and reduces effectiveness. Many mums see output improve within a few sessions simply by switching to a better-fitting flange, without changing anything else.
Do I measure the areola when checking flange size?
No — measure only the nipple base in millimetres, then add 2–4 mm to find your starting size. For example, a 19 mm nipple typically fits a 21–22 mm flange. During pumping, only a very small amount of areola should be drawn in.
Can flange size affect comfort with a wearable breast pump?
Yes — more so than with traditional pumps. A wearable sits inside your bra throughout the session with no way to adjust mid-pump, so a poor fit is felt more acutely and directly affects output. Getting your size right before your first session makes a significant difference to both comfort and consistency.
What is the most common breast pump flange size?
24 mm is the default included with most pumps, but many mums actually need 19–22 mm. Assuming the default fits without measuring is one of the most common causes of discomfort and low output. If you need smaller, silicone flange inserts are a practical solution that works with most pump brands.
Is a 24mm flange too big for me?
For most mums, yes. Research and clinical experience both suggest the average nipple diameter is closer to 16–18 mm, meaning the 24 mm default is too large for the majority of people who use it. A simple way to check: after a pumping session, if you can see significant areola tissue being pulled into the tunnel alongside your nipple, the flange is too big. Measure your nipple base in millimetres and add 2–4 mm — for most mums this lands somewhere between 19 mm and 22 mm.
How do I measure my nipple size without a ruler?
A few everyday references can help: an Australian 5-cent coin is approximately 19 mm across, and a 10-cent coin is approximately 24 mm — useful as a quick comparison. You can also cut a strip of paper, wrap it around your nipple base, mark where it meets, then flatten and measure the strip against any straight edge. For the most accurate result, measure after a feeding or pumping session when your nipple is relaxed, not engorged.
How often should I replace my breast pump flange?
There's no fixed schedule, but it's worth rechecking your fit every few weeks — especially in the first three months postpartum when breast tissue and nipple size change most significantly. Replace your flange if you notice cracks, discolouration, or the plastic feels less firm than when new. If pumping that previously felt comfortable starts feeling tight, loose, or uncomfortable without another obvious cause, a worn flange may be contributing.