If you have ever experienced nipple pain while pumping, reduced milk output, or discomfort that makes you dread your next session, there is a good chance your flange size is the culprit. Flange fit is one of the most overlooked factors in successful pumping, and getting it right can make an immediate and significant difference in both comfort and output. Here is everything you need to know to find your correct size.
What Is a Flange?
The flange, sometimes called a breast shield, is the cone-shaped piece that fits over your nipple and areola and connects to the pump tubing. When you pump, your nipple is drawn into the tunnel of the flange by suction. If the tunnel is too wide, too much areola gets pulled in along with the nipple, causing friction and discomfort. If the tunnel is too narrow, your nipple rubs against the sides and cannot move freely, which reduces milk flow and causes pain. A correctly sized flange allows your nipple to move comfortably in the tunnel with a small amount of space around it — approximately 1 to 3 millimeters.
How to Measure Your Nipple
Flange sizing is based on nipple diameter, not breast size. To measure, use a soft measuring tape or a printed nipple ruler and measure the diameter of your nipple at its base — not including the areola. Measure after a feeding or pumping session when your nipple is its most natural shape. Your nipple diameter in millimeters corresponds directly to the size of the flange tunnel you need. For a visual guide and printable sizing tool, visit the Storkpump Flange Sizing Guide.
Keep in mind that your two nipples may not be identical in size, and your nipple size can change during the course of your breastfeeding journey as your body changes. It is worth re-measuring if you notice a change in comfort or output.
Signs Your Flange Is the Wrong Size
A flange that is too large will cause the areola to be pulled excessively into the tunnel alongside the nipple. This creates friction, can reduce suction efficiency, and often causes a rubbing sensation. You may also notice that the nipple does not seem centered in the tunnel during pumping. A flange that is too small will cause the nipple to rub against the sides of the tunnel. This is one of the most common causes of nipple pain while pumping and can lead to swelling, redness, and reduced milk output over time. In either case, the fix is straightforward — adjusting to the correct size typically resolves discomfort quickly. Check the Storkpump FAQ for more guidance on pump fit and accessories.
Standard Sizes and What to Do If You Fall Between Sizes
Most breast pumps come with one or two standard flanges, typically in the 24mm to 28mm range, which fits many but not all nipple sizes. If you measure outside of the included sizes, sizing inserts or alternative flange options are widely available. Sizing inserts fit inside a standard flange to reduce the tunnel diameter, which is a cost-effective option for moms who need a smaller size. Many pump brands including Spectra and others carried by Storkpump offer a range of flange sizes and compatible inserts.
Does Flange Size Affect Milk Supply?
Yes, and this is why getting the right fit matters beyond just comfort. When a flange does not fit correctly, milk is not removed as efficiently from the breast. Over time, incomplete milk removal signals your body to produce less milk. Many moms who struggle with unexplained supply issues find that correcting their flange size makes a meaningful difference. If you have addressed flange fit and are still experiencing supply concerns, connect with a Storkpump IBCLC at askanIBCLC@storkpump.com for personalized support.
Soft Silicone Flanges
In recent years, soft silicone flanges have become increasingly popular as an alternative to traditional hard plastic options. Many moms find them more comfortable, particularly for longer pumping sessions. They are available for most major pump brands and come in a range of sizes. If you have been using hard plastic flanges and find them uncomfortable even at the right size, silicone flanges are worth trying.
Frequently Asked Questions
How do I know what flange size to start with?
Start by measuring your nipple diameter in millimeters as described above, then match that measurement to the recommended flange size for your pump brand. Most brands add 1 to 3mm to the nipple diameter for the flange tunnel size to allow for comfortable movement. The Storkpump Flange Sizing Guide walks you through this process step by step.
Can my flange size change over time?
Yes. Nipple size can change during pregnancy, in the early postpartum period, and as breastfeeding progresses. It is a good idea to re-measure if you notice discomfort developing after a period of comfortable pumping, or if your output starts to decrease without an obvious cause.
Do both nipples need the same flange size?
Not necessarily. Many moms have slightly different nipple sizes on each side and use different flange sizes for each breast. Measure both nipples individually and use the size that is correct for each side.
Is flange sizing different for wearable pumps?
Yes, some wearable pumps use a different sizing system or proprietary flange design. Always refer to the sizing guide specific to your pump model. Browse wearable pump options on Storkpump to find models with flexible sizing options.
Sources
- Berens, P., Eglash, A., Malloy, M., & Steube, A. M. (2016). ABM Clinical Protocol #26: Persistent pain with breastfeeding. Breastfeeding Medicine, 11(2), 46-53. https://doi.org/10.1089/bfm.2016.29002.pjb
- Centers for Disease Control and Prevention. (2026). About breastfeeding. https://www.cdc.gov/breastfeeding/php/about/index.html
- U.S. Food and Drug Administration. Breast pumps. https://www.fda.gov/medical-devices/consumer-products/breast-pumps
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