A complete guide on how to choose the right flange size.

Get the most out of your pumping sessions by ensuring the perfect fit with our Flange Size Guide! Your comfort and milk output matter, and the right flange size can make all the difference.

What is a Breast Pump Flange?

A flange, also known as a breast shield, is the funnel-shaped piece that fits over your nipple during pumping. It creates a seal between your breast and the pump, enabling efficient milk extraction.

Why is Flange Size Important?

A flange, also known as a breast shield, is the funnel-shaped piece that fits over your nipple during pumping. It creates a seal between your breast and the pump, enabling efficient milk extraction.
Step 1

Gather your tools.

You’ll need a soft measuring tape, ruler, or flange sizing tool provided by your pump manufacturer. Do not pump before measuring, but do gently stimulate your nipple to ensure an accurate measurement.

Step 2

Measure your nipple.

Using the tool, measure the diameter of your nipple in millimeters at its widest point. Focus on the base of your nipple, excluding the areola. Measure both horizontally (left to right) and vertically (up and down) and use the larger measurement.

Step 3

Refer to the guide.

Use the guide below to determine your recommended flange size. Keep in mind that breast shield size can vary between manufacturers, so make sure to follow the guide provided by the manufacturer.

Flange Size Chart by Manufacturer

Pro Tip: For first-time pumps, seeing a lactation specialist can be helpful in determining the correct flange size for your nipple size as well as areola density and fullness, and can make a big difference in your pumping experience.

The COMFY Test

Follow the following COMFY guidelines recommended by lactation consults to ensure the right fit:


Center Nipples Move Freely.

When using the correct flange size, your nipple should move freely in and out of the tunnel without touching the sides. Any rubbing or discomfort indicates that the flange could be too small, potentially leading to irritation or reduced milk flow.

Only a Little Areola is Pulled Into the Tunnel.

During pumping, only a small amount of areola tissue should be pulled into the tunnel along with your nipple. If too much areola enters the tunnel, the flange may be too large, leading to decreased suction and discomfort.

Motion of Your Breast is Gentle and Rhythmic.

As the pump operates, your breast should move back and forth gently with each cycle. If there’s too much movement or if your breast feels restricted, it could indicate an improper fit.

Feels Comfortable Breast Pumping.

Pumping should never cause pain or tenderness. If you experience discomfort, it’s essential to adjust the flange size to ensure a comfortable pumping experience. Discomfort could result from using a flange that is either too small or too large.

Yields Well-Drained Breasts.

After pumping, your breasts should feel noticeably softer and lighter, indicating that the majority of the milk has been effectively removed. If your breasts still feel full after pumping, it may suggest an incorrect flange size or inadequate milk removal.

Look out for the following signs that may suggest your flange size might not be right for you.


Pain or Discomfort.

If you experience significant pain or discomfort while pumping, it could indicate that your flange size is too small or too large.

Delayed Let-Down.

If it takes more than 2-3 minutes for your milk to start flowing after you begin pumping, it could be a sign that your flange size is not optimal.

Recurrent Plugged Ducts.

If you frequently experience plugged ducts despite other causes being ruled out, it might be due to an incorrect flange size.

Visible Damage or Irritation.

Look for redness, swelling, or abrasions on your nipple or areola after pumping, which could indicate friction or improper fit.

Breasts Still Feel Full After Pumping.

If your breasts still feel heavy and full after a pumping session, it may indicate that your flange size is too small, preventing complete milk removal.

No Change in Milk Supply or Decreased Output.

If you notice no improvement or a decrease in milk supply over time, despite regular pumping, it could be due to an incorrect flange size.

Need help?

Every Ounce is here to help! Feel free to contact us to learn more about how to measure your flange size or to inquire about getting a free breast pump through insurance!

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