Breast Pump Flange Sizing Guide

Using the correct size breast pump flange (aka breast shield) can be very important.  Mums who express often complain of discomfort with expressing 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


There are 3 elements to flange sizing:

1. The size of your nipple

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 size that was very close to the actual diameter of their nipples.  But there are also some who prefer a size bigger, some even a size smaller.  Some also seem to have a 'magic spot' - a place where more milk flows even if the flange seems a little uncomfortable.  And 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.  See below for some common signs that your flange is too big.


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

You are welcome to contact me if you have any questions.  If you are sending a video showing you using your current size 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 bother showing me the nipples xx minutes into a session - once they have swelled up in the wrong size it gives me no information

*Up to January 2022 I have seen 2 people who needed 24mm flanges (April 2022 - I have now seen 1 more person need a 24mm and 2 people who truly needed 27mm flanges), although I think that once some swelling goes down they will be able to go down further.  I have estimated that I have helped size ~500 people to date (27/4/22).

Flange Sizing Guide (4).png

NOTE - measuring is just the first step. You may need to try multiple sizes before finding the one that works for you.


Click on the ruler (with the Maymom logo) to download a print at home nipple ruler (ignore that it says to add 2-4mm - I have revised that advice and will be changing the information soon)

Please be very careful to read the measurement closely and measure a few mm above the areola - I find a lot of people are measuring themselves too big.

nipple ruler1.PNG

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)

  • It takes more than a minute to get a letdown (note that 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 the sides of the flange

Sign your flange is TOO SMALL:

  • The nipple does not move freely in the first minute - this is the only reason to size up, in my experience

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

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.


Note that your nipple may get larger over time as it is drawn out from feeding/expressing, or it could decrease as any swelling subsides so your sizing may change. 


Personal and professional experience

Maymom® sizing  guide

Medela® breastshield sizing tool -