Important to know before you start reading - the information below might be quite different to what you have been told by other midwives and/or lactation consultants.  Please understand that I am not saying this to be argumentative or 'arrogant'.  I have quite literally made expressing my business, since March 2016.  My ultimate goal is to ensure mothers (and their families) are getting good expressing advice and support.  I have been sizing mothers in person and virtually since August 2020, and estimate that I see 5-10 mothers per week.  This information is based on what I have observed and heard from them.  Other midwives/lactation consultants probably do not have this level of experience with sizing and may be using outdated information from breast pump companies.

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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 is not 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...

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

 

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

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

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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

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

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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.

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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'.

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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. If a midwife/lactation consultant has measured your nipples and given you a flange size, they unfortunately have not given you the correct information.​  The only way to know the correct size is to test out sizes - like trying on shoes.  I have plenty of examples of 'eye balling' a nipple, thinking it is a certain size, but once we test it out we have to go up or down depending on how the nipple responds

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But here is some information to gauge if your flange is too big or too small

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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

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Sign your flange is TOO SMALL:

• The nipple does not move freely in the first minute (if the nipples swells up and then stops moving, the flange is too big to start with)

• The nipple does not fit into the hole at all

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

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

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Sometimes 1-2mm too big can feel worse than 3 or more mm too big - if there is any space between the nipple and the side of the flange in the first few seconds of turning the pump on, it is probably too big

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I estimate that at least 95% of all mothers need SMALLER than 18mm, with the majority of them needing 15-17mm

 

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.

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

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*To date (12/01/2025) I estimate I have seen >1200 mothers in person and via video - I have seen about 4 mothers who truly needed 24mm flanges and about 7 who truly needed 27mm flanges (although I think that once some swelling goes down they will be able to go down further).  I have now seen 2 mothers who truly needed bigger than 27mm, but not bigger than 30mm