top of page

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

Last updated 1/10/2022

Let’s talk flange sizing – it is something that could make or break your expressing journey.

Firstly, let me tell you about my personal experience with using the wrong sizes

I was told to start expressing by an IBCLC for my daughter when she was 3 days old. My milk hadn’t come in and it looked like she had lost too much weight. I was initially told that I needed 27mm flanges. A week later at a follow-up appointment, I was told I needed 30mm flanges because I wasn't expressing much (10mls max). Having very little expressing knowledge I believed them (this was despite working in NICU for 8 years already - it certainly wasn't something we learned much about).

By ~10 days post birth I was barely expressing 10-20mls/session. Slowly it increased to about 30mls/session but would not increase any further. Using the 30mm flanges hurt and I kept going back to the 24mm flanges that I had as they were slightly more comfortable. I would also get more out (only about 10mls more and no more than 30mls total).

Around 6 weeks post birth, I saw a different 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. And she suggested that I try 36mm flanges. In between all this, another IBCLC had agreed that 30mm flanges seemed to be correct. So, 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’.

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 6/day whereas the minimum should 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 8mths of exclusive expressing (I did my last session 3 days before my daughter was 10mths old) I saw numerous posts about flange sizing. And I came to realise just how important it was to get the correct size and that unfortunately those 3 IBCLC’s who had told me I was a 30-36mm were wrong.

“Your flange should fit your nipple like a shoe”

Professional experience with flange sizing

In March 2016 I started selling Spectra breast pumps as an authorized stockist. Flange sizing quickly became a ‘passion’ (some might say obsession!). I realized that so many new mothers were being told the same thing as me – you need a 27, 30, or 36mm flange.

I started stocking Maymom flanges around the same time as the Spectra breast pumps and I did a survey on the Exclusive Expressing group to work out what volume of stock I should be ordering. Most said they were between a 19 and 27mm flange, so that is mainly what I stocked. Over time I realised I was selling more 19mm’s than anything else and I was getting numerous requests for 17's and 15’s.

In approx 2017, a fellow IBCLC from the USA, who I know went through similar expressing journey to me (she is in the Exclusive Expressing group), did a similar survey to me just recently and interestingly the vast majority said they were a 17, 19 or 21mm - below is a summary of her survey.

Results of the informal Facebook survey done by a fellow IBCLC. This is a screenshot taken from a presentation I did for a Breastfeeding conference in 2020 - hopefully I can prevent some from giving out the wrong advice!

I have also seen numerous clients who have been told to use flanges that are too big for them with damage (usually around the areola or base of the nipple) and poor output. The vast majority of the time they say that using smaller flanges (ie ones that fit properly) is more comfortable and help them yield more milk.

In late August 2020 I started allowing customers in Perth to come test out different sizes in person. Up to then, I was 'eyeballing' sizes, using the guide of 'measure the diameter of the nipple (before expressing) and add 4mm'.

I was surprised to see that most people found sizing that was even smaller than I originally thought was more comfortable.

Over the last 2 years, I estimate I have seen close to 700 mothers either in person or via video and I have learned a lot about sizing. I am not really someone to brag about myself, but I often hear 'you were recommended in xyz group' or 'my LC told me to contact you for sizing', etc, and I get quite a few follow up messages along the lines of ‘this size is so much more comfortable’ and/or ‘I’m getting so much more with this smaller size flange’, so I am pretty confident in my recommendations now

Here is what I have found:

Signs that your flange is TOO BIG:

  • Your nipple swells up while expressing (this is often why people think they need bigger - the nipple should not swell up that much)

  • Your breast loses contact with the flange while expressing

  • Milk leaks out the bottom of the flange (note that no flange is designed to suction onto the breast and be handsfree)

  • It takes more than a minute to get a letdown (this one might be subjective - there might be other reasons that you have a slow letdown, but in most cases, milk flows almost instantly with the correct size)

  • Your breasts still feel full after expressing

  • It feels 'tight' but there is still room between the nipple and the sides of the flange

Sign your flange is TOO SMALL:

  • The nipple does not move freely in the first minute

  • The nipple does not fit into the hole at all

These are the only reason to size up, in my experience

"But I was using a 24 or 27mm flange and it was 'too tight' or it was 'swelling up' - why would I go down a size?"

This is something I hear ALL THE TIME!

When you are using a size that is too big your breast tissue (usually the areola, sometimes the actual breast) gets pulled into the funnel - this makes everything swell up. The tissue is literally swelling to meet the diameter of the flange you are using. At some point, the tissue can no longer swell and so it feels like you are using the right size. However, very little of the areola should be entering the flange - so there would be no to very little swelling at all.

It actually seems that the less areola that gets pulled in, the better, even if this means that the nipple is rubbing on the side - as long as it is moving freely.

Something interesting I have realised recently is that sometimes just 1 size too big can cause the most pain and least output - often people buy a size, then a size bigger, then contact me for assistance. They are surprised when I size them smaller than the first size they bought - they say 'but the 17mm (for example) was more so much more painful than the 19mm, but it still doesn't feel right, so I thought I needed bigger...'. Nope, because BIGGER IS NOT ALWAYS BETTER!

I just doubled my output and my breasts finally feel empty for the first time since she was born...I honestly can't believe it...I got 40mls at 3.45pm [with 24mm flanges]....Then at 7.40pm 100mls with the 17mm. Unbelievable! And no lumps after for once

This quote is from a recent client who was amazed that she needed smaller (17mm) as her lactation consultant told her to get 28mm flanges (Spectra do 28mm, Medela and Maymom do 27mm)

Visual guide of flanges that are too big, too small, and just right - note, however, that the only way to know what size you need might be to try out different sizes

I no longer recommend measuring nipples, either before or after expressing - I have had too many incidences where people have measured and about flanges only to find they are incorrect, or come to me saying they needed 'xx' size only to find they need a size or 2 smaller.

I no longer stock any flanges bigger than 27mm - in the 2 years I have been sizing mothers in person and via video, I have not seen anyone need bigger than 27mm. I have only seen about 5 each need 27mm or 24mm, a handful need 21mm, and probably 90% need less than 19mm (the most common sizes seem to be 13mm, 15mm, and 17mm).

So then why did my IBCLC/midwife tell me that I needed much bigger? Because unfortunately, they do not know how to size properly. And I am saying this not to confuse you or to criticize other health professionals – please keep in mind that breast pump flange sizing is not a part of the midwifery training or even the lactation consultant training. I had to learn this information from a Facebook group and then trial and error of helping others with sizing....

Like I said above, there are always exceptions to rules and it might take some trial and error. Using the analogy of it fitting like a shoe - you wouldn't walk into a shoe shop and just buy whatever takes your fancy in the size you think you are, or based on measurements, you would try it on, walk around the shop, and make sure it feels comfortable. The same goes for your flange. And just like shoe fittings, you could get home, use the flange for a bit and realise it is still not quite right. (Keep in mind that sometimes there might not be a perfect fit though.)

If you need help with flange sizing you are welcome to see me in person (in Perth) or send me a video of you using your current size - there is no charge for this. Or you can try my flange lending service - found under 'Shop Now' at the top of the page Send me a text or email if you need more assistance - 0405427998 or


Featured Posts
Recent Posts
Search By Tags
Follow Us
  • Facebook Basic Square
  • Twitter Basic Square
  • Google+ Basic Square
bottom of page