How to Size Your Breast Pump Flanges at Home: A Step-by-Step Guide

Quick answer

To find your correct flange size, measure the diameter of your nipple (not the areola) in millimeters and add 2–4 mm for comfortable fit. Use a printed sizing tool or a measuring tape, and test with a sizing kit before committing to a pump. Wrong sizing can reduce milk output and cause pain.

If you’ve ever pumped and felt a pulling or pinching sensation, or noticed your milk output suddenly drop, your flange size might be the culprit. Flanges—also called breast shields—are the funnel-shaped parts that fit over your nipple, and getting the size right is one of the easiest ways to make pumping more comfortable and effective.

The good news: you don’t need a professional fitting. With a simple measurement and a bit of trial, you can find your correct flange size at home. Here’s how to measure, what to look for, and how to use a sizing kit to get the best fit for your wearable pump.

Why Flange Size Matters

The flange creates a seal around your nipple and applies gentle suction to remove milk. If the tunnel is too narrow, your nipple rubs against the sides, causing friction, pain, and even cracked skin. Too wide, and too much areola gets pulled in, which can reduce suction efficiency and leave milk behind.

A correct fit means your nipple moves freely inside the tunnel with a small amount of areola pulled in, without pain. This maximizes milk output and makes sessions more comfortable. Since every person’s nipple size can change during pregnancy and breastfeeding, it’s worth checking your size periodically.

• Nipple size can change, so re-measure if you experience discomfort or reduced output.

How to Measure for Flange Size at Home

You’ll need a ruler with millimeter markings, or you can print an online sizing tool. Measure the diameter of your nipple at the base, without including the areola. Do this when your nipples are at their most relaxed, not after pumping or cold exposure, because they can temporarily change size.

Add 2–4 mm to your nipple diameter to get your flange size. For example, if you measure 17 mm, a 19–21 mm flange is ideal. Some brands, like Elvie, offer inserts in smaller sizes, so even if the standard flange is 21 mm, you can adjust for a 15, 17, or 19 mm fit.

• Always measure both nipples—they might be different sizes.

Using a Sizing Kit to Test Fit

A sizing kit gives you multiple insert sizes to try without committing to a full set of flanges. These kits are especially useful for wearable pumps, where the flange size can’t be easily swapped out and you want to get it right the first time.

The Breast Pump Sizing Kit from Elvie includes five insert sets, a sizing tool, and a guide to help you find your size. It also gives you access to a Sizing Specialist, so you can get personalized support. Try the recommended size first, then adjust up or down based on comfort and output.

• If you’re between sizes, start with the larger size—it’s easier to adjust down than up.

Signs You’ve Got the Wrong Flange Size

Pay attention to how pumping feels and looks. Symptoms of a wrong flange size include pain or pinching during pumping, nipple blanching (white spots after pumping), reduced milk output compared to usual, and skin chafing or redness around the nipple. Also, if you see areola tissue pulled deeply into the tunnel, the flange is likely too large.

If any of these signs appear, try a different size. Sometimes the fix is as simple as using an insert or cushion, like the Elvie Nipple Cushions, which can improve fit and comfort without needing a new flange.

• A wrong flange size can also cause cracked or sore nipples, so don't ignore persistent discomfort.

Step-by-Step Guide to Sizing Your Flange

1. Gather your tools: Get a ruler with millimeter markings or a printing-friendly sizing tool. If using a sizing kit, lay out the inserts and guide. Check that your ruler measures mm; not all rulers do.
2. Measure your nipple at the base: Measure the diameter at the widest point, excluding the areola. Do this at a neutral time, not right after pumping or when cold. Measure both nipples, as they can differ.
3. Add 2–4 mm to get your target flange size: Your flange should be slightly larger than your nipple to allow for a little movement. For example, 17 mm nipple → 19–21 mm flange. If between sizes, go larger—you can use inserts to fine-tune.
4. Test with a sizing kit or inserts: Use a sizing kit to try the size you calculated. Pump a few times and evaluate comfort and output. Slight adjust up or down based on feel and milk flow.
5. Check the fit during pumping: Your nipple should move freely in the tunnel without pain. Look for symptoms like pinching, pain, or reduced output. If you see any symptoms, re-measure and try a different size.
6. Re-size periodically: Nipple size can change with breastfeeding stages. If you notice new discomfort, re-measure to see if your size has changed. Regular checks help maintain comfortable, effective pumping.

Products to Help You Get the Right Fit

• Breast Pump Sizing Kit: Includes five insert sets, a sizing tool to easily find your size, Pump Sizing 101 guide, and support via a Sizing Specialist. This kit takes the guesswork out of flange sizing, so you can test multiple sizes at home and find the perfect fit without buying multiple pump parts.
• Elvie Nipple Cushions (2 pack): Soft-silicone nipple cushions to enhance fit, available in 15 mm, 17 mm, and 19 mm, designed for use inside 24 mm Breast Shields. If you measure smaller than the standard shield size, these cushions let you adjust the fit comfortably, improving both comfort and milk output.

Getting the right flange size transforms pumping from a chore into a comfortable, efficient part of your day. Take a few minutes to measure, test with a sizing kit, and adjust as needed. Your breasts—and your milk stash—will thank you.