Size does matter....but bigger is not always better

Information last updated in March 2026 (I only got around to updated this blog today)

This article is based on what I’ve learned from more than 2500 in‑person and virtual sizing consults since 2020, and from specialising in expressing since 2016. It was one of the first blogs I wrote and over time the information has changed, but the overall messaging has not - bigger is not always better - and in most cases, it’s actually the opposite.

If you see older content on my website or anywhere else with my name on it that contradicts this, please know it is outdated. I’d appreciate it if you let me know so I can update or remove it.

Flange sizing can make or break your expressing journey - some just do not realise it until their output starts to drop or the pain/damage becomes unbearable.

My Personal Experience (Why I Became Obsessed With Sizing!)

I was told to start expressing by an IBCLC for my daughter when she was 3 days old. My milk hadn’t started increasing yet and it looked like she had lost too much weight. I was initially told by that midwife and IBCLC that I needed 27mm flanges.

A week later at a follow-up appointment, I was told I needed 30mm flanges by a different midwife/IBCLC because I still wasn't expressing much (10mls max per session). Having very little expressing knowledge I believed them - this was despite working in NICU for 8 years and 2 years as a midwife before giving birth - it certainly wasn't something we learned much about!

Using the 30mm flanges hurt and I kept going back to the 24mm flanges because they were slightly more comfortable. I would also get more out with the 24mm - only about 10mls more and no more than 30mls total each session.

Around 6 weeks post birth, I saw a different midwife/IBCLC who wanted to help me increase my supply and suggested I try a different brand of breast pump while I waited for my Spectra to arrive. She suggested that I try 36mm flanges. In between all this, another IBCLC had agreed that 30mm flanges seemed to be correct. So, in total, 3 IBCLCs had said I needed 30 or 36mm flanges.

I tried the 36mm flanges but quickly went back to the 24mm’s – they were definitely more comfortable, and I got more with them. Although it was painful to express, I pushed through, wanting to give my daughter whatever breast milk I could get.

About 2 weeks before I ordered my Spectra I tried a friend's electric pump (a brand that you can buy off the shelves in Big W or Target) which had ‘comfort massaging inserts'. I got the most I had ever got – 40mls! When another friend told me about the Spectra I ordered it with their ‘massaging inserts’, which made a 24mm flange into about a 22mm.

I also joined an Exclusive Expressing / Pumping Facebook group on her recommendation. After a week or so I posted my story, desperately wanting to increase my supply. The main thing I was told was to increase the number of sessions I was doing - I was only doing 4-6/day whereas the minimum I was told should be 8. But someone in there also recommended checking my flange size. I didn’t pay too much notice to that suggestion as I was now using the Spectra 24mm’s with the inserts (which took them down to a 22mm) and it was somewhat comfortable, and I was seeing an increase.

Over the next 8 months of exclusive expressing I saw numerous posts about flange sizing, and I came to realise I could have probably been using 17mm or smaller. Unfortunately those 3 IBCLC’s who had told me I was a 30-36mm were wrong - maybe not on purpose, but lacking correct knowledge.

Maybe if I had been using the correct size each session would not have taken me 45mins just to get enough...the prevailing advice back then was 'measure and add 4mm'

As I started my business, I realised most mothers were smaller than the 'standard' 24mm but were being told to use bigger, like me. I didn't realise just how small until I started sizing people in person in 2020.

This experience is why flange sizing became my specialty - in fact, one colleague calls me The Nipple Whisperer for how well I can size people!

Professional Experience: What Thousands of Mothers Have Taught Me

Since 2016, I’ve specialised in expressing and flange sizing. Over time, I noticed the same pattern: Parents were consistently being told they needed 24mm, 27mm, 30mm, or even 36mm flanges - and almost always, these sizes were far too big.

In 2020, I began allowing Perth clients to test sizes in person, because I got tired of trying to convince people to try smaller, and then everything changed.

I quickly saw that:

• Most people needed much smaller sizes than expected

• Measuring is highly inaccurate

• Comfort and output improved dramatically with smaller sizes

• In person testing the only reliable method

Over the years I become more confident in telling people that they need smaller flanges, and just how small they need to go. I have become so confident that mothers do no need routinely need bigger than 21mm that I have stopped selling bigger sizes on my website - I still have these sizes in person, but I need to confirm that they are correct for the person before selling them.

I stopped counting at around 1500 mothers sized, but these are some statistics for bigger sizes:

• Only ~4 people truly needed 24mm

• Around 7 people truly needed 27mm

• Only 2 people needed larger than 27mm (but not bigger than 30mm)

This means less than 1% of mothers need flanges in the 24–30mm range.

Most people fall between 13mm and 18mm.

The most recent statistics I have for smaller flanges are:

• 70% need 15 - 17mm

• 20% need 14mm or smaller

• This means 90% need 17mm or smaller

• Only 5% need 18-19mm

• <1% need 24mm or bigger

Click here for my flange sizing guide for more information on sizing

Why Measuring Doesn’t Work

If anyone tells you to “Measure your nipple and add 4mm.”  

Or: “Pump for 5 minutes, measure, and add 1–2mm.”

Or they have done this with you in person....

Both are inaccurate

This is because:

• Nipples swell to meet the flange you’re using, artificially increasing the measurement (it would be like trying a t-shirt over a jumper and then thinking that is your regular t-shirt size). You DO NOT need to allow room for the nipple to swell

• Printable and/or silicone sizing guides don’t show how your nipple responds to vacuum

• Measuring doesn’t account for comfort, movement, or milk flow

• Many people mistake areola for nipple, leading to oversized recommendations

Flange sizing is like shoe fitting — you must try sizes in person, not just rely measure.

I've seen mothers need anything between 0-10mm diffferent from their 'measurements' - there is no correlation between even measuring at rest and using that exact size. Even sometime I 'eyeball' someone and then need to go up or down quite a few millimetres from what I initially thought. This is because vacuum can either draw out more nipple that we cannot see initially or elongate it and make it 'skinnier'. Or some people have a 'magic spot' where they need the flange to be to yield milk, even if it looks 1-2mm too big or too small.

Signs Your Flange Is Probably Too Big

• Nipple swells significantly while expressing

• Breast loses contact with the flange

• Milk leaks out the bottom

• Letdown takes longer than a minute

• Breasts still feel full after expressing

• It feels “tight” but there’s still space around the nipple

• You need high vacuum to get milk flowing

Signs Your Flange Is Probably Too Small

• Nipple cannot move freely in the first minute

• Nipple cannot fit into the tunnel at all

These are really the only reasons to size up.

Although measuring and visual guides are not that accurate, this is sort of what you flange should look like

Common Misunderstandings (Ie. Not Reasons to Size Up)

• “The nipple is rubbing” - often this is actually areola, not nipple - it is actually good for the nipple to be touching the sides of the flange, as long as it is moving freely

• “The nipple is swelling, so I need more room to accommodate that” - swelling usually means the flange is too big

• “It feels tight” - often caused by too much areola being pulled in

A surprising comment I hear many times is that the flange feels too tight, yet to me it still looks too big, yet they feel that something 3+mm feels better, but still does not give great output. Over the years I've realised many cases, this is because just a small amount of areola is being pinched between the side of the flange and the nipple. Going smaller just by 1-2mm usually helps immensely.

Why Bigger Isn’t Better

When a flange is too big, breast tissue (usually areola) gets pulled into the tunnel. This causes swelling, discomfort, and poor milk flow. The tissue swells to “fill” the flange, making it look like the right size or that you need bigger - but it isn’t.

Less areola pulled in = better comfort + better output.

Real‑World Example

A few years ago someone message me saying her lactation consultant told her use 27mm flanges. She was struggling with pain and low output. There was a lot of back and forth in messages as I thought she was closer to a 17mm (we were sizing via videos), she was very reluctant to try 17s, but finally agreed. After switching to them she messaged:

“I just doubled my output and my breasts finally feel empty for the first time since she was born… 40ml with 24mm, then 100ml with 17mm. Unbelievable!”

Not everyone will get results this dramatic of course (although I have seen a few similar cases over the years), but it shows how powerful correct sizing can be.

Why Health Professionals Often Give Larger Sizes

This isn’t criticism - flange sizing simply isn’t taught in midwifery or IBCLC training. Most professionals rely on outdated manufacturer guidelines or “handed‑down” advice. The same definitely goes for doctors - they do not get any breastfeeding education in their training, unless they have specifically gone to seek it themselves.

And why is 24mm included with just about every breast pump? Because this was the size that was determined as 'standard' 60-70 years ago when breast pumps were invented, with no real-world research...slowly the advice is changing - it is rare that I now have people asking for 30mm flanges (still happens, but not as frequently), and many hospitals and private IBCLCs are contacting me to learn more about smaller flanges.

Flange sizing is a niche skill that requires hands‑on experience, not theory or measuring.

How Can You Be Sized Properly

If you’re in Perth, you’re welcome to come try sizes in person.

If you can't come in person or are interstate, overseas, or want to test sizes at home, you can use my Flange Lending Service — borrow up to three sizes to test before deciding. Available on the online store

Or you can send me a video, just make sure to follow these guidelines:

1. First few seconds with the nipple at rest in the flange

2. Side view

3. No hands‑free bra

4. Turn pump to massage/letdown mode for a few seconds

Please don’t send videos taken mid‑session - swollen nipples don’t give accurate information.

Need More Help?

Flange sizing is free for those in Australia and New Zealand in person or by video. If you are outside Australia or New Zeland please contact me to find out the costs and Ts&Cs.

You’re welcome to contact me anytime: 0405 427 998  info@cherishedparenting.com.au