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If you’re anything like me, at some point in your life you’ve had the experience of something that was just “not a good fit” – the wrong partner, the wrong job, the wrong size outfit or bra. What started out as “those adorable pumps that match my Holiday dress PERFECTLY” are now just a painful memory in the Goodwill box in the garage. Ladies, those shoes might still be in your closet if you had just gone with a slightly wider toe and a somewhat smaller heel!! Just like so many other things in life a good fit can mean the difference between a great experience and a painful one.

Choosing correctly fitting flanges, also known as breast shields, is an imperative step when you first begin to use your breast pump. Breast pump flanges fit directly over your nipple to form a seal around the areola, which creates a vacuum that gently draws your nipple into the tunnel for milk extraction.

Incorrectly sized breast pump flanges (or breast shields) can lead to soreness, blocked milk ducts and ultimately lack of milk production. Learning how to figure out what size flange is right for you can help you avoid  problems before they begin.

The standard flange is going to be 24mm – so when measuring, you can start with that. Center your nipple and gently hold the breast shield in place. While doing this you are going to want to put your pump in the “expression mode” and be looking for several things when you turn the pump on.

What to Look For

    1. Does your nipple rub the sides of the tunnel causing discomfort? Does it look red or irritated? Your flange could be too small.
    2. Is a large part of your areola being pulled into the tunnel with your nipple (possibly turning white or red?) Your flange could be too big.
    3. After pumping do you still feel “full” or like you have not expressed all your milk?


These can all be signs of the wrong size flange! When your breast pump flange size is correct, your nipple is centered and moves freely in and out of the tunnel. It should mimic baby more like a gentle suck/tug, NOT be painful or cut off blood flow in any way. Make sure to perform this on both sides in case you need two different flanges. Having a good fit will allow for a good start to a comfortable and productive pumping experience!

Will My Flange Size Change?

Keep in mind that breast pump flange fit can change between the time you give birth and when you actually begin using a breast pump. What fits when you began breast pumping may change, so it is important to check your breast pump flange fit from time to time.

Not only is the fit essential, but properly maintained flanges ensure the effectiveness of the breast pump. Replacing breast pump flanges (and other breast pump supplies) can extend your pump's life. Check to see if your insurance will cover new breast pump supplies.

The 'COMFY' Test

When determining the right breast pump flange size, remember the word ‘COMFY’.  This term was specifically designed to help moms just like you remember five guidelines about breast pump flange sizing.

  • C – Centered nipple which moves freely.

    Your nipple should move freely in the breast pump flange tunnel. You should not experience any rubbing. (If you do, this indicates your breast pump flange is too small).

  • O – Only a little or no areola tissue is pulled into the tunnel.

    If your nipple is able to move freely in the breast pump flange tunnel you will notice there will be a gentle pulling movement in the areola each time your breast pump cycles. If there is no movement in the areola, your breast pump flange is more than likely too small.  On the contrary, if there is a lot of movement or a large amount of your areola is pulled into the tunnel, your breast shield is probably too big.

  • M – Motion of the breast is gentle and rhythmic with each cycle of the pump.

    You should see gentle breast movement with each cycle of the pump just as you do with your nipple. Gentle breast movement indicates your breast is getting proper stimulation while pumping.

  • F – Feels comfortable pumping.

    Using a breast pump should not be uncomfortable for you nor should it cause nipple pain or tenderness. If you experience pain or discomfort, more than likely you have an ill-fitting breast pump flange.

  • Y – Yields a well-drained breast.

    Your breasts should feel soft after each use of your breast pump.

We hope this breast pump flange size chart has helped you determine if your breast pump flanges fit correctly. If you have any questions regarding breast pumps or breast pump flanges, give us a call at 844-867-9890.


Information provided in blogs should not be used as a substitute for medical care or consultation.


Susan Hudspeth

About the Author

I am 47 years old - I am originally from L.I. New York but moved to NC when I was 23 years old and never left! My breastfeeding background includes breastfeeding all three children for a period of 7 years total from 1991-1998. I was also very involved in my local La Leche League during that time. I cannot say enough good things about breastfeeding and how important and rewarding it is for both mom and baby!

Learn more about Susan!