Flange Size Calculator

For mothers who pump breast milk, finding the right flange size is one of the most critical factors for a comfortable and effective pumping experience. An ill-fitting flange can not only cause pain and nipple damage but also significantly reduce the amount of milk you can express. This guide is designed to demystify the process of measuring for a breast pump flange, helping you find the size that works best for your body.

What is a Breast Pump Flange?

The flange, sometimes called a breast shield, is the plastic, cone-shaped part of the breast pump that fits directly over your breast. Its primary function is to create a seal around your areola and nipple, allowing the pump's suction to effectively draw milk from the breast.

Flanges are not one-size-fits-all. They come in various sizes, measured in millimeters (mm), which corresponds to the diameter of the flange's tunnel. Using the correct size ensures that your nipple can move freely within the tunnel without rubbing against the sides, and without pulling too much of your areola in with it.

Why is the Right Flange Size So Important?

• Comfort and Pain Prevention: This is the most immediate benefit. A flange that is too small will cause your nipple to rub and chafe, leading to pain, cracking, and bleeding. A flange that is too large can pull too much of the areola into the tunnel, causing pinching and discomfort.
• Milk Output: A proper fit is essential for maximizing milk expression. An incorrect size can compress or block milk ducts, preventing your breasts from draining fully. This can lead to a decrease in milk supply over time, as supply is driven by demand (i.e., how much milk is effectively removed).
• Preventing Clogged Ducts and Mastitis: When breasts are not drained properly due to a poor flange fit, it can lead to clogged milk ducts. If not resolved, a clogged duct can progress into mastitis, a painful breast infection.

How to Measure for Your Flange Size: A Step-by-Step Guide

The size of the flange you need is based on the diameter of your nipple *before* pumping. Many women find their nipples change size throughout their breastfeeding journey, so it's a good idea to re-measure periodically.

1. Gather Your Tools: You'll need a ruler or a flexible measuring tape that has millimeter markings. You can also find printable flange sizing tools online.
2. Stimulate Your Nipple: Gently roll your nipple between your thumb and finger to encourage it to become erect. This helps you get a more accurate measurement of its typical size during pumping.
3. Measure the Diameter: Carefully measure the distance straight across the base of your nipple. **Do not include the areola**, which is the darker, circular area of skin surrounding the nipple.
4. Calculate Your Flange Size: The ideal flange size is slightly larger than your nipple measurement to allow for comfortable movement. A general rule of thumb is to add **2 to 4 millimeters** to your nipple's diameter.

Your Nipple Diameter (in mm) + 2-4 mm = Your Recommended Flange Size (in mm)

Example: If your nipple measures 19 mm across, you would likely need a 21 mm or 23 mm flange. Since most brands sell flanges in standard sizes (e.g., 21mm, 24mm, 27mm), you would start by trying the 21 mm size.

Checking Your Fit: Signs of a Good vs. Poor Fit

Measurement is the best starting point, but the ultimate test is how it feels and performs when you pump.

Signs of a Good Fit:

• Your nipple is centered in the flange tunnel.
• Your nipple moves freely back and forth within the tunnel.
• Only a small amount of your areola is pulled into the tunnel with each suction.
• You experience a comfortable, gentle tugging sensation, not pain.
• Your breasts feel empty and soft after pumping.

Signs Your Flange May Be Too Small:

• Your nipple rubs against the sides of the tunnel.
• You feel pinching or pain.
• Your nipple appears white or blanched after pumping.
• Your milk flow seems slow or incomplete.

Signs Your Flange May Be Too Large:

• A significant portion of your areola is pulled into the flange tunnel along with your nipple.
• You feel pain or discomfort around the areola.
• Your breast doesn't feel adequately drained.

Final Thoughts

Don't be discouraged if the standard flanges that came with your pump are not the right size—most women need a different size. Many brands sell a wide range of flange sizes separately. Investing the time to find your correct size is one of the best things you can do to make your pumping journey a more positive and productive one. If you continue to experience pain or have concerns about your milk supply, don't hesitate to reach out to a lactation consultant for personalized support.