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Breast Pump Flange Sizing Guide

Most breast pumps these days come with flanges in 24mm flanges (the part that goes over the breast), some bigger, never smaller (as far as I know).  If you are expressing with the 'standard' size and have no issues, then you don't need to fix something that isn't broken, but keeping this information in mind in case you do run into an issue might be a good idea. 


If you are having issues...

Using the correct size breast pump flange (aka breast shield) can be very important. 


The most common complaints are discomfort and/or low output.  Over the years I have seen numerous times that finding the correct size flange can help decrease this discomfort and potentially increase output. 

Here is an article I wrote about why it is so important, plus more information on sizing

I have been letting mums try out sizes in person since August 2020.  I have also offered a video service for those who cannot come in person, as well as a lending service. I estimate that I see 5-10 mothers per week for sizing, so this information is based on seeing 100s, if not well over 1000, mothers.  


The information below is based on what I have seen and the feedback I have had over the years.

There are 3 elements to flange sizing:

1. The size of your nipple and how it responds to vacuum

2. How the flange feels when you are pumping

3. How your body responds to it

Up until August 2020 I was following the advice of 'measure the diameter and add 4mm', and that was the end of the story....

Then I started allowing customers to test out flanges in person. 


I quickly realised that the majority prefer a flange size that was very close to the same size of their nipples.  Some seem to have a 'magic spot' - a place where more milk flows even if the flange seems a little uncomfortable.  Sometimes people test out different sizes, buy one, realise that it is not quite right, and need to try others again - ie it may take some trial and error.

Since August 2020 I have not seen anyone need bigger than a 21mm flange*.  If you have been told that you need a flange of 20/21mm or larger I would strongly recommend you double (or triple or even quadruple if needed) check using this information.  Note that this is only if you are having issues.  If your output is great and you are comfortable, then you don't need to 'fix something that isn't broken'.

I do not recommend measuring your nipples - I am finding that a lot of people are overestimating their sizing when basing it just on measuring.  But if you do want to measure, make sure you measure your nipple when it is erect (do not pump first, just stimulate it slightly) and measure about 2-3mm from the base, ie where it meets the areola - but honestly, you shouldn't based your flange size on measuring alone. 

Signs that your flange is TOO BIG:

  • Your nipple swells up while expressing

  • 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)

  • You need to use a high vacuum to get any milk out (note that high vacuum should not be needed and in fact could inhibit milk flow)

  • 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

Note: it appears to be OK for the nipple to be rubbing along the sides of the flange - as long as it moves freely


If you are in Perth you are welcome to come try out different sizes in person.  If you are interstate, or want to borrow different sizes for a bit longer, I now have a new option - Flange Lending Service - borrow up to 3 different sizes to test out before deciding on a size. Available Australia wide.  Click here for more information.  


You may also send me a video of you using your current flange. Please follow these instructions - 

1. Start with the nipples at rest in the flanges, preferably from the side (please take off hands free bras as theses obstruct the view)

2. Turn the pump onto massage or letdown mode (or the fastest mode) for a few seconds

Note - do not send videos showing me the nipples xx minutes into a session - once they have swelled up in the wrong size it gives me no information.

You are welcome to contact me if you have any questions. 

*To date (12/05/2024) I estimate I have seen >1000 mothers in person and via video - I have seen about 4 mothers who truly needed 24mm flanges and about 6 who truly needed 27mm flanges (although I think that once some swelling goes down they will be able to go down further).  I have still not seen anyone need bigger than 27mm.

Flange sizing guide, Spectra flange, Medela
Flange sizing, Spectra, Medela, how to know your flange size is correct
Flange sizing, Spectra, Medela, flanges are too big

I have found the rule of "measuring after expressing for 5mins and adding 1-2mm" can be inaccurate as the nipple will swell to meet the flange you are currently using, which artificially increases the size (it's like trying on a t-shirt over a jumper - you either wouldn't do it or know that you can go down a few sizes).  Also, the guides that make you cut out holes and place them over your nipple may not be completely accurate either - they do not show how your nipples respond to vacuum, which can be an important step.

A note on elastic nipples -

I often have emails/phone calls from people saying they think they have 'elastic nipples' and do I have a product that will help. Often their nipple is reaching almost the very end of the funnel or may even be hitting it.  Some have heard that Pumpin Pal flanges will help them.  Over time I have realised that a lot of people who think they have elastic nipples are actually using the wrong size, usually much too big.  Before you spend lots of money on other flanges that may be the wrong size, please use this guide to figure out if you are using the right size.  I also highly recommend that you try regular (ie hard, straight) flanges before trying something like the Pumpin Pal or Lacteck flanges - not because I want to make more money, but because in most cases the regular flanges work better when they are the correct size.

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