What is a Breast Pump Flange?
A breast pump flange (also called a breast shield) is the funnel-shaped plastic piece that fits directly over the nipple and areola during breast pumping. It creates a seal around the breast and channels suction to draw the nipple into a tunnel where milk is expressed. The flange is the critical interface between the pump and the body, and its fit directly affects pumping comfort, efficiency, and milk output.
Flanges come in various sizes, typically measured by the internal diameter of the tunnel opening in millimeters. Most breast pump manufacturers include one or two standard flange sizes with their pumps (commonly 24 mm and 27 mm), but these standard sizes do not fit all women. Research suggests that up to 70% of pumping mothers use an incorrectly sized flange, which can lead to reduced milk supply, nipple pain, tissue damage, and premature weaning.
The importance of proper flange fit cannot be overstated. A correctly sized flange should allow the nipple to move freely within the tunnel without rubbing against the sides, while not allowing excessive areola tissue to be drawn in. When the flange fits properly, pumping should feel like a gentle tugging sensation without pain, pinching, or discomfort. The nipple should emerge from a pumping session looking normal in color and shape, without any white spots, creases, or swelling.
How to Measure Your Nipple
Accurate nipple measurement is essential for determining the correct flange size. Follow these steps:
- Time your measurement: Measure your nipple in its resting state (not stimulated or cold), ideally before or between pumping sessions. Some lactation consultants recommend measuring after pumping, as the nipple may swell slightly during use and you want a flange that accommodates this
- Use the right tools: Use a flexible measuring tape or a printable nipple ruler (available from many breast pump manufacturers). You can also use a caliper for precise measurements. A simple ruler held against the base of the nipple works in a pinch
- Measure the diameter: Measure straight across the base of the nipple (where it meets the areola), not including the areola itself. This is the widest part of the nipple, not the tip
- Measure both sides: Nipple sizes can differ between breasts. Measure both nipples and note if you need different flange sizes for each side
- Record in millimeters: Write down your measurement in millimeters. Most nipple diameters range from 12 mm to 23 mm, with the average being around 16 mm
The additional 3 to 4 mm provides clearance for the nipple to move freely within the tunnel during pumping without friction, while being snug enough to prevent excess areola from being pulled in.
How to Choose the Right Flange Size
Once you have your nipple measurement, add 3 to 4 mm to determine your ideal flange tunnel diameter. Then match this to the closest available standard size. Here is a general guide:
| Nipple Diameter (mm) | Recommended Flange (mm) | Standard Size to Try |
|---|---|---|
| 9–13 mm | 12–17 mm | 15 or 17 mm (small/extra-small) |
| 14–17 mm | 17–21 mm | 21 mm |
| 18–20 mm | 21–24 mm | 24 mm |
| 21–23 mm | 24–27 mm | 27 mm |
| 24–26 mm | 27–30 mm | 30 mm |
| 27+ mm | 30–36 mm | 36 mm |
Keep in mind that these are starting points. Every breast is unique, and factors such as tissue elasticity, engorgement level, and pumping duration can affect the ideal fit. You may need to try adjacent sizes to find the most comfortable option. Many manufacturers offer flange sizing kits that allow you to test multiple sizes before committing.
Signs of Wrong Flange Fit
| Symptom | Likely Cause | Solution |
|---|---|---|
| Nipple compressed or pinched in tunnel | Flange too small | Try the next size up (e.g., 21 to 24 mm) |
| Areola sucked into the tunnel | Flange too large | Try the next size down |
| Sore, red, or cracked nipple after pumping | Flange too small | Size up and check suction level |
| White nipple tip or blanching | Flange too small (vasospasm) | Size up; apply warmth after pumping |
| Marked redness or soreness on areola | Flange too large | Size down to reduce areola friction |
| Low milk output despite feeling full | Poor flange fit (either direction) | Re-measure and try a different size |
| Nipple swelling during/after pumping | Flange too small or suction too high | Size up and reduce suction setting |
| Comfortable at start, painful near end of session | Nipple swelling into a too-small flange | Consider sizing up half a size |
Common Flange Sizes
Breast pump flanges are manufactured in a range of standard sizes. While each manufacturer may offer slightly different options, the most common sizes available across major brands are:
| Flange Size (mm) | Category | Typical Nipple Diameter | Availability |
|---|---|---|---|
| 15 mm | Extra Small | 9–11 mm | Specialty / third-party |
| 17 mm | Small | 12–13 mm | Specialty / third-party |
| 19 mm | Small | 14–15 mm | Select brands |
| 21 mm | Standard Small | 16–17 mm | Most major brands |
| 24 mm | Standard Medium | 18–20 mm | Included with most pumps |
| 27 mm | Standard Large | 21–23 mm | Included with most pumps |
| 30 mm | Large | 24–26 mm | Most major brands |
| 36 mm | Extra Large | 27+ mm | Select brands |
If your calculated flange size falls between two standard sizes, it is generally better to round up to the larger size to prevent compression. Third-party companies like Maymom, Pumpin Pal, and BeauGen offer insert cushions and alternative flange shapes that can help customize fit within standard-size flanges.
Tips for Comfort and Efficiency
- Use nipple cream or coconut oil: Apply a small amount of lanolin-based nipple cream or food-grade coconut oil to the inside of the flange tunnel before pumping. This reduces friction and makes the pumping experience more comfortable
- Center your nipple: Ensure the nipple is centered in the flange tunnel before starting the pump. An off-center nipple can cause uneven friction and reduce efficiency
- Start on low suction: Begin pumping at the lowest comfortable suction setting and gradually increase. Higher suction does not always mean more milk; excessive suction can cause tissue damage and actually decrease output
- Check for elasticity changes: Nipple size can change over time due to hormonal shifts, weight changes, and breastfeeding progression. Re-measure every few months or if you notice changes in comfort or output
- Consider silicone inserts: If you are between sizes, silicone flange inserts can reduce the effective tunnel diameter by 1 to 3 mm, providing a custom fit within a larger standard flange
- Replace flanges regularly: Plastic flanges can develop micro-scratches over time that harbor bacteria and increase friction. Replace flanges every 3 to 6 months or sooner if you notice discoloration, cloudiness, or rough textures
- Seek professional help: If you continue to experience pain or low output despite trying different sizes, consult a board-certified lactation consultant (IBCLC). They can observe your pumping technique and provide hands-on sizing assistance
Frequently Asked Questions
What size flange do most women need?
While 24 mm is the most commonly included flange size with breast pumps, many women actually need a smaller size. Studies show that the average nipple diameter is approximately 16 mm, which corresponds to a 19 to 21 mm flange. This means a significant number of women are using flanges that are too large. The best approach is to measure your nipple diameter and calculate your size rather than assuming the included flange will fit correctly.
Can my flange size change over time?
Yes, nipple size can change throughout your breastfeeding journey. Hormonal fluctuations, engorgement, weight changes, and the natural process of breastfeeding can all affect nipple dimensions. Many women find they need to resize their flanges at several points: during the initial postpartum period, when milk supply regulates (around 6 to 12 weeks), and if they become pregnant again while still breastfeeding. It is good practice to re-measure every 2 to 3 months.
Do I need different flange sizes for each breast?
It is quite common for nipples to be different sizes on each breast, just as breast size itself is often asymmetric. If your nipple diameter differs by 2 mm or more between sides, you may benefit from using different flange sizes for each breast. Most pump manufacturers sell individual flanges, making it easy to mix sizes. Using the correct size for each breast can significantly improve comfort and milk output.
How do I know if my flange fits correctly?
A properly fitting flange allows the nipple to move freely within the tunnel with approximately 1 to 2 mm of space on each side. During pumping, you should see the nipple sliding smoothly in and out without rubbing against the tunnel walls. The areola should not be pulled significantly into the tunnel (a small amount of areola movement is normal). After pumping, the nipple should appear normal in color without white spots, creasing, swelling, or redness. Pumping should feel like gentle tugging, not painful pinching.
What if my nipple measurement falls between two standard sizes?
If your calculated flange size falls between two standard sizes, try the larger size first. It is generally better to have slightly more space than to compress the nipple in a too-small flange. If the larger size draws in too much areola, consider using a silicone insert or cushion to reduce the effective tunnel diameter. Some third-party manufacturers offer flanges in 1 mm increments, providing more precise sizing options than the standard 3 mm jumps between sizes.