Categories: Breastfeeding, Pumping
March 11, 2024
Last updated on August 18, 2026
Finding the right size for your breast flange or shield will help you ensure appropriate milk output and have the most comfortable pumping sessions possible. Don’t know what size breast shield you need? Find out more below!
What is a flange?
A flange, or breast shield, is the cone shaped funnel that fits directly over your nipple, areola, and breast. When using the correct size and shape, it forms a seal between your breast and the plastic or silicone that then creates a vacuum to extract milk.
Many manufacturers will also make smaller inserts or cushions that go within an existing breast shield size. These reduce the opening of the tunnel where the nipple enters. They are often less expensive than a full flange or breast shield, but may not always be as effective.
Why flange size matters
Using the correct size flange or breast shield will help optimize milk output. If a flange is too small, it could restrict the tissue from moving appropriately. If the flange is too large, it may not remove all the milk, which could contribute to a lower milk supply. Using an ill-fitting flange can also cause nipple or breast pain or injury.
In a recent flange size survey conducted by Acelleron with over 490 respondents, over 75% of respondents agreed with the following statement: “I got a different size that was not in the original pump kit and had a better experience with my pump after,” emphasizing the positive impact of using the correct size.
Breast shield size is based on your nipple size, not your breast/chest size. Sizes range from about 9mm to 36mm+, depending on the brand. The measurement refers to the diameter of the flange tunnel, where the nipple enters, not the overall opening of the flange.
Breast pumps typically come with 1 or 2 sets of breast shields, most likely around 21-24mm. Many manufacturers now include multiple silicone inserts to accommodate smaller sizing. In addition to the included size(s), some brands like Cimilre, have special guarantees to help you get the size you need by offering you an additional size option, free of charge! Outside of these guarantees, additional sizes typically require an out-of-pocket purchase or using a possible insurance benefit covering replacement parts.
How to measure your flange size
To determine the best flange size for you, you’ll need to measure your nipple.
- Start by lightly stimulating your nipple with gentle touch. One method is to place a finger and thumb on opposite sides of your nipple- think top and bottom- and gently hold (do not squeeze or press firmly) for about 10 seconds.
- Next, move to the other two sides and hold for another 10 seconds. This is sometimes called the “Sparks Tip!*”
- Then, using a ruler, measure the diameter of the tip of your nipple in millimeters. We recommend measuring vertically (up and down) and horizontally (left to right) and using the average, somewhere in the middle, of those 2 measurements. Do not include measurements for your areola, the larger part around your nipple.
- Once you have your nipple diameter, it is recommended to try sizes around it (-1mm up to +2mm). You may be able to select the closest size flanges or inserts offered by your pump manufacturer.
- For example, if your nipple tip measures 10mm vertically and 12mm horizontally, you could use 11mm as your starting point for sizing.
Examples:
- Using a Cimilre S6, measuring 14mm: Next size is 16mm flanges.
- Using Elvie, measuring 16mm: You could try the 15mm or 17mm inserts.
- Using a Lansinoh SmartPump 3.0, measuring 20mm: Try 19mm inserts or 21mm flanges.
- Using a Medela PNS Pro, measuring 18mm: You could try the 18mm flanges.
- Using a Spectra S2, measuring 19mm: Next size is the 20mm flanges.
- Using a Willow, measuring 14mm: You could try the 13mm or 15mm inserts.
- Using a Zomee Z2, measuring 22mm: Try 21mm flanges or inserts or 24mm flanges.
If the sizes offered by the manufacturer of your breast pump do not work for you, reach out to them directly and ask what they suggest! Using off-brand replacement parts may undermine the warranty for your pump and/or impact the suction strength and/or effectiveness. However, some manufacturers are ok with you using off-brand flanges or inserts if they DO NOT offer the size you need. It’s best to check!
Keep in mind, breasts are not identical. Each breast/nipple may require a different size flange. In fact, your flange size may even change throughout your pumping journey. Before you replace your pump parts, it’s a good idea to remeasure to confirm you are still using the correct size.
It’s not just the numbers
The size of your nipple is not the only thing that matters. You also want to pay attention to what happens to your nipple once the pump is on and suction is applied to your body. Everyone’s body reacts differently- stretching longer vs wider. It is okay if your nipple touches the side of the flange tunnel, as long as it still moves easily and does not cause any friction, discomfort, or damage.
How to know you have the proper flange fit
Signs of an incorrect fit:
- Significant pain while pumping
- Breast/chest/areolar/nipple discomfort between pumping sessions
- A delayed let-down (2+ minutes)
- Recurrent plugged ducts, with other causes ruled out
Signs of a correct fit:
- The flange fits comfortably around your nipple and breast/chest
- Only your nipple and little to none of your areola enter the tunnel when pumping (because nipples are not perfect circles!)
- Any movement of the nipple against the side of the tunnel is fluid and comfortable
- Your letdown occurs within 1-2 minutes of pumping, at most
- You see milk spraying out or a significant flow
- After pumping, your breasts feel soft and emptied
- Your milk supply remains the same or improves
- Overall, your pumping sessions are comfortable and free of pain
Flange shapes
It is important to note that while there are different sizes, there are also different shapes to consider.
Below is an image from Maymom, a manufacturer of many different flange sizes and shapes, showing some of the most common shapes available:
Different flange shapes help support and accommodate a variety of breast shapes, proportions, and sizes of lactating individuals. You will also see these different shapes and styles from common breast pump manufacturers in their included collection kits.
Silicone inserts & flanges
Silicone inserts/flanges can interact with your body differently than a hard plastic shield and may not work as well. When trying these, the following may be helpful:
- Silicone items may need to be slightly larger than a hard plastic option to fit comfortably (by about 1-2 mm)
- Using lubrication may help with nipple movement and comfort. Make sure to only apply a small amount to the tunnel of the flange, as it should only be on your nipple while pumping, not the surrounding areola or breast.
- Do not try a silicone insert without the guidance of a lactation professional if you have any concerns about your milk supply
A final note
Finding and using the correct size flange is important to ensure your pumping experience is as successful and comfortable as possible. Spending time to determine your flange size will go a long way toward helping you meet your breastfeeding and pumping goals. If you have questions about your flange fit, pumping, and more, check out our breast pump education resources. For additional support, reach out to a lactation provider in your area.
Still looking for a breast pump? We can help you get your free breast pump through insurance!
This blog includes, but is not limited to, recommendations from the study completed by Lisa A. Anders, PhD, RN, IBCLC, Jeanette Mesite Frem, MHS, IBCLC, RLC, CCE, and Thomas P. McCoy, PhD, PStat
Click here to learn more about The Flange FITS™ Guide created by Jeanette Mesite Frem, Babies in Common. The guide is available in 21 languages!
*The Spark’s Tip was created by Monique Sparks from Durham, NC, who does flange fitting exclusively: https://www.beyondbirthlactation.com/about
**This post contains affiliate links, which means Acelleron may receive a commission if you make a purchase using these links.