Getting your flange size right is one of the most impactful things you can do for comfortable, productive pumping, and the good news is you can measure yourself at home in just a few minutes. If pumping has been uncomfortable or your output has been lower than expected, your flange size is the first thing worth checking. Here is a simple, step-by-step guide to measuring correctly.
Quick Reference: What You Need to Know About Flange Sizing
Before you measure, here are the key facts that make the whole process clearer:
- Flange size is based on nipple diameter, not breast size or areola size.
- You measure the nipple only, not including the surrounding darker areola.
- The correct flange tunnel is typically 1 to 3mm larger than your nipple diameter, leaving a little room for the nipple to move freely.
- Both sides may differ, so measure each nipple individually.
- Size can change over time, so re-measure if comfort or output changes.
For a printable visual tool to guide you, the Storkpump Flange Sizing Guide walks through the process with measurements you can reference at home.
What You Will Need
Measuring at home requires very little. You can use a soft fabric measuring tape, a ruler with millimeter markings, or a printable nipple ruler, which many pump brands and sizing guides provide. Measuring tools that show millimeters are ideal since flange sizing is done in millimeters. Have a mirror handy if it helps you see clearly, and pick a private, comfortable spot where you can take your time.
Step-by-Step: How to Measure Your Nipple
Follow these steps for the most accurate measurement:
Step 1: Measure when your nipple is at its natural shape, ideally a few minutes after a feeding or pumping session when it is not compressed or swollen. Measuring at rest gives the most accurate baseline.
Step 2: Measure straight across the base of your nipple at its widest point, from one side to the other through the center. Measure only the nipple itself, where it meets the areola, not the darker areola tissue around it.
Step 3: Note the measurement in millimeters. This number is your nipple diameter.
Step 4: Repeat on the other side. It is common for the two nipples to differ slightly, and you may need a different flange size for each breast.
Step 5: Add 1 to 3mm to your nipple diameter to determine your starting flange tunnel size. For example, a nipple measuring 17mm typically starts with a 19 to 20mm flange. Many brands provide their own sizing recommendations, so check the guidance for your specific pump as well.
How to Know If Your Size Is Right
Measuring gives you a starting point, but the real test is how the flange performs during a session. With a correct fit, your nipple moves freely in the tunnel without the areola being pulled in significantly, you feel a strong but comfortable pulling sensation rather than pinching or rubbing, and your nipple looks round and its normal color after pumping rather than swollen, blanched, or creased. If your nipple rubs the sides of the tunnel, your flange is likely too small. If a lot of areola gets pulled in, it is likely too large. Watching your nipple during a session, ideally with a clear flange, is one of the most reliable ways to confirm fit. The Storkpump Learning Center has more guidance on troubleshooting fit during pumping.
What to Do If You Are Between Sizes
It is very common to measure between standard sizes, and there are good solutions. Most pumps come with one or two standard flange sizes, often in the 24mm to 28mm range. If you measure smaller, silicone sizing inserts fit inside a standard flange to reduce the tunnel diameter, which is an affordable way to fine-tune your fit without buying entirely new flanges. If you fall between two sizes, starting with the smaller option and testing it for comfort and output is often the better approach, since a slightly snug fit tends to cause fewer problems than one that is too loose. Many pumps carried by Storkpump, including Spectra models, offer a range of flange sizes and compatible inserts.
Why Getting This Right Matters
An incorrect flange size does more than cause discomfort. It reduces how efficiently milk is removed, which over time can lower your supply because incomplete emptying signals your body to produce less. Many moms who struggle with unexplained low output or persistent nipple pain discover that the simple fix was their flange size all along. Taking a few minutes to measure correctly at the start of your pumping journey, and re-checking periodically, sets you up for more comfortable and productive sessions. Storkpump is committed to helping you pump with confidence, which starts with the right fit. Browse insurance-covered breast pumps on Storkpump to find a model with flexible sizing options, and visit our FAQ page for more on accessories and replacement parts.
Frequently Asked Questions About Measuring Flange Size
How do I measure my flange size without a ruler?
If you do not have a millimeter ruler or measuring tape, many pump brands and sizing guides offer a free printable nipple ruler you can use at home. The Storkpump Flange Sizing Guide provides a reference tool to help you measure accurately. In a pinch, a millimeter ruler from a stationery set works as well.
Should I measure before or after pumping?
Measure when your nipple is at its natural, resting shape, which is usually a few minutes after a feeding or pumping session when it is not compressed or swollen. Measuring immediately after suction can give an inflated reading. A relaxed nipple gives the most accurate baseline for sizing.
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 worth re-measuring if you notice new discomfort after a period of comfortable pumping, or if your output begins to drop without another clear cause. Re-checking your fit periodically is a good habit.
Do I really need different sizes for each breast?
Possibly. Many moms have slightly different nipple sizes on each side, and using the correct size for each breast individually can improve both comfort and output. Measure each nipple separately, and do not assume both sides are the same. Using two different flange sizes is completely normal if that is what your measurements show.
Learn More with Storkpump
For a complete visual walkthrough of flange sizing, visit the Storkpump Flange Sizing Guide. When you are ready to choose a pump with sizing options that fit your needs, browse our full collection of insurance-covered breast pumps.
Sources
- Academy of Breastfeeding Medicine Protocol Committee. (2016). ABM Clinical Protocol #26: Persistent pain with breastfeeding. Breastfeeding Medicine, 11(2), 46-53. https://www.bfmed.org/protocols
- 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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