If pumping has been painful or your output has been disappointing, there is a good chance your flange size is part of the problem. Incorrect flange fit is one of the most common and easily overlooked causes of pumping discomfort and reduced milk output, and it is also one of the most fixable. Here is how to tell whether your flange is too big, too small, or just right, and exactly what to do about it.
What the Right Flange Fit Looks Like
When your flange fits correctly, your nipple moves freely in the tunnel with only a small amount of space around it, approximately 1 to 3 millimeters on each side. During pumping, your nipple should be centered in the tunnel and move in and out with the suction rhythm without dragging the areola in alongside it. Pumping should feel like a strong but comfortable pulling sensation, not pain. After a session, your nipple should look round and its normal color, not blanched, swollen, or creased. Use the Storkpump Flange Sizing Guide to measure your nipple diameter and find your starting size.
Signs Your Flange Is Too Large
A flange that is too large creates a gap between the nipple and the tunnel walls that allows excessive areola tissue to be pulled in alongside the nipple. You may notice your areola being drawn significantly into the tunnel during pumping, which creates friction and reduces the effectiveness of the seal. Other signs include a rubbing or chafing sensation rather than a clean suction feeling, redness or soreness on the areola rather than the nipple itself, and suction that feels less consistent even at higher settings. Output can decrease over time because the pump is not creating efficient pressure against the nipple and milk ducts.
Signs Your Flange Is Too Small
A flange that is too small causes the nipple to rub against the sides of the tunnel with every pump cycle. This is one of the most common causes of nipple pain during pumping and can lead to swelling, soreness, and bruising over time. Signs include pain or pinching during pumping, your nipple looking swollen or blanched after a session, reduced milk output despite adequate suction settings, white or red marks on the nipple after pumping, and difficulty triggering let-down. If you have been pumping through pain assuming it is normal, checking your flange size should be the very first step.
How to Measure for the Right Size
Flange sizing is based on your nipple diameter, not your breast size. To measure, use a soft measuring tape or a printed nipple ruler and measure across the base of your nipple at its widest point, not including the areola. Your nipple diameter in millimeters corresponds directly to the flange tunnel size you need, with most brands recommending adding 1 to 3mm to your nipple diameter for the correct tunnel size. The Storkpump Flange Sizing Guide includes a step-by-step walkthrough and sizing tool you can print at home.
Measure both nipples individually since they are often slightly different sizes. Your nipple size can also change over time as breastfeeding progresses, so re-measuring is worth doing if you notice a change in comfort or output.
What to Do Once You Know Your Size
Most pumps come with one or two standard flanges, typically in the 24mm to 28mm range. If your measurement falls outside that range, sizing inserts are available for many pump brands and are a cost-effective way to reduce the tunnel diameter without buying new flanges. Many Spectra, Zomee, and other pumps carried by Storkpump offer a range of flange sizes and compatible inserts. If you are unsure which size to order after measuring, a Storkpump IBCLC can help at askanIBCLC@storkpump.com.
Frequently Asked Questions
Can the wrong flange size reduce my milk supply over time?
Yes. 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. Many moms who struggle with unexplained supply drops find that correcting their flange size makes a meaningful difference. Visit the Storkpump Learning Center for more guidance on supply and pumping technique.
My nipple size falls between standard sizes. What should I do?
Start with the size closest to your nipple diameter plus 1 to 2mm and test it for comfort and output. If you are between sizes, sizing inserts can help fine-tune the fit. A lactation consultant can also assess your fit in person or via video and make a specific recommendation based on what they observe during a pumping session.
Should I re-measure my nipples after giving birth?
Yes. Nipple size can change during pregnancy and in the postpartum period as your body adjusts. Measuring after your milk comes in, typically around days 3 to 5, gives you a more accurate baseline than measuring during pregnancy. Re-measure any time you notice a change in pumping comfort or output.
Are silicone flanges better than plastic ones?
Many moms find soft silicone flanges more comfortable than traditional hard plastic, particularly for longer sessions. They are available for most major pump brands and come in a range of sizes. If you are using the correct size plastic flange but still experiencing discomfort, trying a silicone version of the same size is a reasonable next step. Check the Storkpump FAQ for more information on accessories and replacement parts.
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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