Medela Breast Shield Sizing Guide

May 14, 2015

Having properly fitted breast shields isn’t just a matter of comfort, it’s important for pumping efficiency too. Using breast shields that are too large or too small can significantly reduce the amount of milk you can pump and cause unnecessary discomfort, which is why choosing the PersonalFit breast shield size that’s right for you is key to pumping success. Been pumping for a while now? Don’t stop reading. Your breast shield size could change over the duration of your breastfeeding journey, so even if you’ve been pumping for several months, it’s possible that you may benefit from a different size.

Understanding Medela’s PersonalFit Sizing

Pumping should not hurt, ever. For maximum comfort and pumping efficiency, Medela offers five different breast shield sizes that are compatible with all Medela breast pumps:

  • 21 mm
  • 24 mm (the size included with all Medela breast pump kits)
  • 27 mm
  • 30 mm
  • 36 mm

24 mm is our most standard size based on data we receive from our healthcare experts. You may need a different size based on your anatomy or other factors, such as needing a different size per breast or the point you’re at in your breastfeeding journey. As their breasts adapt over the course of lactation, some moms may find that they need a larger size breast shield, while other may benefit from a smaller size.

In order to find your optimal size, you can measure your nipple diameter:

  1. Using a ruler or measuring tape, measure the diameter your nipple at the base (across the middle) in millimeters (mm). 1 cm = 10 mm. Do not include your areola.
  2. Based on your measurement, use the guide below to determine your PersonalFit breast shield size.

PersonalFit breastshield guide MedelaSo, for example: If your nipple measures 16 mm in diameter, your recommended PersonalFit breast shield size is 21 mm because the 21 mm shield fits nipples up to 17 mm in diameter. If your nipple diameter measures 24 mm, your recommended size would be 30 mm.

A note about nipples:

Be sure to understand the difference between your nipple and areola. Your areola is the darkened area on your breast around your nipple. Your nipple is the projection of your mammary gland from which milk is produced.

Medela Nipple Anatomy

Testing Your Breast Shield Size

To confirm which size breast shield is the best fit, you should watch the nipple movement during pumping. Your breast shield size also depends on your breast tissue and skin elasticity (not just nipple size alone). In order to determine if your PersonalFit breast shield is the right size, you can perform a quick test using your pump and the breast shields that came with it.

  1. Start with the 24 mm breast shields that were included with your pump (or the size determined by measuring your nipples).
  2. Center your nipple and gently hold the breast shield against your breast. Be careful to not press breast shields too hard against your breasts when pumping – this can block your milk ducts!
  3. Adjust your pump’s vacuum for your Maximum Comfort Vacuum* to achieve optimum suction level, turning the vacuum up until slightly uncomfortable and then down a notch. (*Maximum Comfort Vacuum refers to the highest but still comfortable vacuum setting while pumping. Pumping at Maximum Comfort Vacuum increases pumping efficiency.)
  4. Refer to the below images while pumping:

Medela Breastshield Fit GuideToo Small

If your breast shield is too small, your nipple will rub along the side of the tunnel. Try a larger size.

Too Large

If your breast shield is too large, your nipple, along with excessive areola, will be pulled into the tunnel. You may benefit from a smaller size.

Correct Fit

When your breast shields fit correctly, your nipple will be centered in the breast shield tunnel and move freely during pumping.

Should You Try a New Size?

If you’re wondering whether your breast shields are the right size for your nipples, ask yourself the following questions:

  • Does your nipple rub the sides of the tunnel to the point of causing discomfort?
  • Do you see excessive areola being pulled into the tunnel?
  • Do you see any redness on or at the base of the nipple during and/or after pumping?
  • Is your nipple or areola turning white during and/or after pumping?
  • Do your breasts still feel full after pumping?

If you answered “YES” to any of these questions, we suggest you consider trying a new size by following the measuring instructions above. If you’re still not sure if you selected the right size, please reach out to a lactation consultant or breastfeeding specialist. You can also contact Medela Customer Service at 1-800-435-8316.

Click here to download the breast shield sizing handout [PDF]

Find Medela products in a store near you.

Select your pump to purchase spare parts directly from our website.

Or, visit one of our online retail partners.

Still have questions? We’re hosting a live chat with Lactation Consultant Irene Zoppi on the Medela Facebook page on Monday, May 18th at 8pm (CT). Click here to learn more and RSVP!

226 thoughts on “Medela Breast Shield Sizing Guide

  1. Do nipple shields wear out quickly? After two weeks of use I’ve found when using it with my pump the shield is allowing my areola to be drawn into the flange. The flange is to large so the shield was adjusting the size for me. It wasn’t doing this before. Is it stretched out now?

  2. Hi,when I pump there is some space left at the bottom and top due to which milk leaks out. Does this mean I need a smaller size?

    • Hi, Aneena. It could mean that. We’d recommend you find a local Lactation Consultant to observe a pumping session so she can give you a personal recommendation on sizing.

  3. Pingback: Mummy Essentials: Breast Pumps (Electric)

  4. My nipples measure 19mm but I’ve been using a 21mm flange because the 24mm flange makes my nipples swell to 4X it’s normal size. Is it okay I’m using a different size than it suggests? Will I still get the best out put?

    • Hi, Ariel. Other factors like breast elasticity can affect which size works best for you. If you have concerns, we recommend finding a local Lactation Consultant to observe a pumping session and give you a personalized recommendation based on your body.

  5. I’ve recently heard a thumping sound while pumping. My output has dropped for pumping but seems the same while nursing.
    I’ve replaced the membrane. What else could it be? The pump is four months old and I use it three times a day.

    • Hi, Mel. If you’re hearing a “thumping” noise from your breast pump, we’d recommend you call our Customer Service team so they can walk through some troubleshooting steps with you to get to the source. They can be reached at 877-633-3522.

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