New Breast Shield Sizing Tool Aids Clinicians

May 2015

Human milk is the number one source of nutrition for infant health and growth, and clinicians do all they can to support mothers in their breastfeeding journey. For mothers who are providing milk to neonatal intensive care infants or for mothers who struggle with providing milk, pumping is an invaluable exercise in their efforts to produce this liquid gold.

What may not be immediately obvious is how breast pump accessories impact successful pumping, and also comfort as well. Pumping should never cause pain. When you are assisting mothers with their breast pumping needs, the following information can help you identify which breast shield size will work best for maximized efficiency and comfort.

Understanding Medela’s PersonalFit™ Sizing

Pumping should not hurt, ever. For maximum comfort and pumping efficiency, Medela offers five different PersonalFit 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. Mothers may need a different size based on anatomy or other factors, such as needing a different size per breast or the point a mother is at in her 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.

Medela’s PersonalFit Flex™ breast shields are the next step in the evolution of our PersonalFit brand. Using innovative Medela Flex technology that adapts to each mother, the unique PersonalFit Flex breast shields feature a 105-degree opening angle, soft rim, and unique oval design that can be rotated a full 360 degrees for reduced pressure, a more natural feeling, and flexibility to find the most comfortable pumping position. PersonalFit Flex breast shields also remove 11.8% more milk per minute. Over time, these breast shields help mothers pump more milk than traditional 90-degree breast shields.

PersonalFit Flex breast shields are also compatible with all Medela breast pumps and are available in four sizes. Please note that Medela offers a 36 mm size in PersonalFit only, not PersonalFit Flex:

  • 21 mm
  • 24 mm
  • 27 mm
  • 30 mm

In order to find an optimal size, you can measure a mother’s nipple diameter:

1. Using a ruler or measuring tape, measure the diameter of a mother’s nipple at the base (across the middle) in millimeters (mm). 1 cm = 10 mm. Do not include the areola.

2. Based on the measurement, use the guide below to determine the correct PersonalFit breast shield size.

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

A note about nipples:

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

Testing Breast Shield Size

To confirm which size breast shield is the best fit, watch the nipple movement during pumping. The breast shield size also depends on breast tissue and skin elasticity (not just nipple size alone). To determine if the PersonalFit breast shield is the right size, you can perform a quick test using the pump and breast shields on mom.

  1. Start with the 24 mm breast shields (or the size determined by measuring the nipples).
  2. Center the nipple and gently hold the breast shield against the breast. Be careful to not press breast shields too hard against the breasts when pumping – this can block milk ducts!
  3. Adjust the pump’s vacuum for Maximum Comfort Vacuum* to achieve optimum suction level by 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 mom is pumping:

breast shield size fit to nipple chart

Too Small

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

Too Large

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

Correct Fit

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

Should She Try a New Size?

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

  • Does the 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 the nipple or areola turning white during and/or after pumping?
  • Do her 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, you can also contact Medela Customer Service at 1-800-435-8316.


To view our new breast shield sizing tool with the above graphics included, click the below link for a PDF you can use, share with fellow clinicians, or even share with mothers in your care.

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



New Purelan™ Lanolin Cream