Breastshield Sizing Guide

how to get letdown while pumping. spectra breast pump
As you get started using your Spectra pump some mums find it helpful to explore breastshield size. Unfortunately, there’s no way to know what your size will be before you start pumping. Your Spectra pumps comes with size 24mm breastshields in the box which will work for most mums at least initially – so don’t panic! When you have had some practice and get used to pumping, you may find that you are better off with a different size.  Getting your best shield fit is ultimately a matter of trial and error to determine what size gives you best comfort and output, regardless of measuring, but hopefully this guide will help you determine that a lot faster.

How to measure your best breastshield size

There are a few different techniques to get an idea of what your shield size will be, but most mums do tend to measure themselves incorrectly or too large – so shoot us a message so we can help! You will need to measure after pumping, as your nipples will swell during pumping. You can use a piece of string to measure around the base of your nipple and then divide by 3.14 (takes you back to circle geometry at school, right?). Or you can try measuring across the base of the nipple with a ruler – this is a lot harder to figure out than it seems though. You want to get end up with the diameter or width of the base of your nipple.  Be careful not to include any swollen areola that is mistaken for nipple in the measurement. This can be tricky so  doing it in front of a mirror or using a smart phone in selfie mode may be helpful.

Your bra / cup size doesn’t matter here

We know you’ve focussed all your life on your cup size, but in this instance it really doesn’t matter. Whatever cup size you are has no impact on your breastshield size needs. We also don’t want to worry about your areola – areola should not enter the breastshield, so you need have a breastshield that is the best size for your nipple only that is not so large that it allows areola to be drawn in. Only the nipple size matters when it comes to sizing your breastshield. If you’ve already started using your breast pump and you’re feeling like you might not be using the right size, here are some pointers:

Signs your shield is too large

  • Your nipple is hitting the end of the shield
  • Your milk output is lower than you expect
  • Areola is being drawn into the breastshield
  • Your nipple has a ‘bunched’ look because some of your areola is being drawn in and bunching up into the nipple.

Signs your shield is too small

  • Your nipple does not fit into the shield to start with
  • Your milk output is low.

Some extra tips to remember

  • Feeling rubbing is not always the sign of a bad shield size. Using a balm, coconut oil or olive oil can really help reduce any rubbing or friction pain.
  • Sometimes painful pumping or too large a shield size can make nipple excessively swollen. This is temporary and may ease with a better shield fit. (Ask us for help if you’re not sure).
  • Not getting any milk when pumping is very often a sign of poor shield fit or positioning (or not using a pump you respond to) not your milk supply. Concluding you don’t have milk because you can’t express any is a common mistake and means you need help!
  • Shield positioning is also super important – it’s helpful you have the best size for you, but more importantly, you need to make sure your shield is positioned well, that your nipple is centred down the shield and that you have a good seal of breast tissue to the breastshield behind the nipple.

What to do if you’re still not sure

If you are having any doubts at all, then please just get in touch. A big part of our day goes in helping mums with shield fit and positioning, and we like to think we know something about it by now! You don’t need to get this right all on your own, so get in touch and we’ll help out. Chat now

20 thoughts on “Breastshield Sizing Guide

  1. Tara says:

    Do you measure after pumping or after breastfeeding?

    As once I’ve feed my little
    One I’m 17.5mm but after expressing my nipple is much more swollen but could be because of a bad shield fit?

    • Spectra Team Australia says:

      Hi Tara, you will need to measure AFTER expressing, as your nipple will swell when pumping, just like it does when feeding, but moreso.

      We need to explore your measurement after pumping to help figure out shield fit options. 🙂

      Hope this helps.

      Spectra team

  2. Lindsay says:

    Is there a way to know what size I would need before my baby is here? I’m not due until February. My dog chewed up the ones that came with my pump so I need new ones regardless

    • Spectra Baby Australia says:

      Hi Lindsay, unfortunately you cannot know shield size till you are pumping after your little one is born and your milk is in, as the act of birth changes your nipples so much. 🙂

      Hope your dog is ok after eating your shield kit parts. 🙂

      • Spectra Team Australia says:

        Hi Lindsay, you will need to measure after pumping, as your nipple will most likely not swell the same with feeding as it does with pumping. 🙂

        Spectra team

  3. Susan Livingston says:

    So the tip of my nipple is quite a bit smaller than the base- before I even get to the areola. Should I try to measure the base?

    • Spectra Team says:

      Hi Susan, we only are interested in measuring the base of your nipple. 🙂

      That diameter – a snug fit, is the best size to try for you to start with.

  4. monique bourne says:

    My nipple only measures 10mm what size should I be getting I’m using a 24mm right now and almost my whole areola gets pulled in

    • Spectra Team says:

      Hi Monique, thanks for your question.

      Are you measuring that size after pumping? Shield sizes start at 15mm, but we do not carry that size.

      If you send us a message to we will make sure you are measuring correctly, and guide you to a best option to try. 🙂

      I will keep an eye out for your message.

  5. Ms Monica Chase says:

    Would be helpful if you included some sort of sizing tool w the pump. Like paper circles. It’s very hard to measure.

    • Spectra Team says:

      Hi Monica, thanks for your comment.

      There is a great nipple ruler made by

      You can find it at

      Have a good weekend.

  6. Christine says:

    Hi, I am having difficulties in express milk using spectra s1. I feel pain around my aerola everytime I express and the milk I express is very slow.and little. Is it because of the breast shield size I am using? Currently I am using both 28mm shield size, my left nipple diameter is around 16mm and the rmight size is around 18mm. Which shield size would u recommend me ?

    • Spectra Team says:

      Hi Christine, thanks for your question.

      There could be a few things happening here, but shield fit seems to be an obvious option to explore.

      If you shoot us a message to we will help you explore your shield size. 🙂

  7. Jessica davis says:

    Not sure what shield size I need. I tried measuring and it was about 1.5 cm. So that correlates to probably the 21mm size which you all do not carry.

    However, I also read you can’t know what size shield you need until after you’ve pumped.

    I am not sure if I should get your brand of breast pump because if I do in fact need a smaller size you don’t have it and then what will I do? Do you have other suggestions or ways of getting a smaller shield size?

    • Spectra Team says:

      Hi Jessica 🙂 Yes we definitely recommend measuring after pumping as nipple size does increase during pumping. We stock a 20mm size, and can recommend compatible alternatives down to a 15mm size from other suppliers if you find that you need a smaller size. Simply drop us an email and we can help you with measuring and finding the right shield size 🙂

    • Spectra Team says:

      Hi Ruth, thanks for contacting us about this.

      You are from the USA, right? You will need to contact [Spectra Baby USA] ( and they will be able to help you.

      Spectra Baby Australia is a different company, and we cannot ship to the USA.

      We also are not able to change the shield sizes that come with our pumps I am afraid. 🙁

      If you need a different size, you can purchase them separately, but we always recommend measuring for the best shield fit to determine the best shield size to order. 🙂

      We have a [blog post here] ( which will be helpful to guide you measuring your shield size. Please PM us if you have any further questions. 🙂

      Have a good week.

  8. janelle says:

    holding the original flange size from the box
    excess areola is being sucked into the flange and boobs dont feed confortable, could it be the funnel size is wrong ?

  9. Meagan says:

    I’m having a punching burning sensation while pumping and afterwards a burning sensation. My nipples are red and very tender! I can’t tell if my flanges are the right size… I’ve tried watching videos but I can’t tell. The very tip of my nipple moves back and forth but the base is stuck in the tube, probably about an inch. I’m using the 24 mm flanges.

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