Breast Pump Sizing 101: How to Measure Your Flange Size at Home

Quick answer

To find your flange size, measure the diameter of your nipple (not the areola) in millimeters and add 1–3 mm for comfort and efficient milk flow. Use a breast pump sizing kit to test inserts and confirm the best fit for your Elvie Pump or other wearable pumps.

Getting the right flange size is one of the most important steps for comfortable and efficient pumping. A flange that's too small can cause friction and pain, while one that's too large may leave milk behind and reduce output. Measuring at home is simple and takes just a few minutes.

Whether you're using an Elvie Pump or another wearable pump, the same measuring principles apply. This guide walks you through each step, highlights common mistakes, and explains how a sizing kit can take the guesswork out of finding your perfect fit.

Why flange size matters

Your flange, sometimes called a breast shield, is the funnel-shaped part that fits over your nipple during pumping. When the fit is correct, your nipple should move freely in the tunnel without rubbing against the sides. This allows the pump to stimulate milk flow effectively while keeping you comfortable.

Using the wrong size can lead to several problems. A too-small flange can cause nipple pain, chafing, and even blisters. A too-large flange may pull in too much areola, which can block milk ducts and reduce output. Many moms also notice a decrease in milk supply simply because they aren't using the right size. Recognizing these wrong flange size symptoms early can save you from discomfort and frustration.

• Pain during pumping often signals a size issue—not a 'normal' part of pumping.
• If you see cracks or fissures on your nipple, check your flange size before anything else.

What you need to measure

You'll need a soft measuring tape or a ruler with millimeter markings. If you have a printed sizing tool, that's even better. You'll also need a quiet moment when your nipples are at their baseline—not just after a feeding or pumping session, as they can temporarily swell.

If you're using an Elvie Pump, note that its flanges come in specific sizes. You can check the size printed on the flange itself. But don't rely on that alone; your size can change over time due to pregnancy, feeding, or weight changes. Re-measuring every few months is a good habit.

• Avoid measuring immediately after pumping, as the nipple may be elongated.
• Use a mirror to see the measurement clearly without bending over.

Step-by-step measuring process

Start by measuring the diameter of your nipple at its base. Do not include the areola. Hold the measuring tape or ruler across the widest part of your nipple. Write down the number in millimeters. If you're between sizes, round up to the nearest whole millimeter.

Next, add 1 to 3 millimeters to that number to allow for comfortable movement. For example, if your nipple measures 17 mm, you'll want a flange between 18 and 20 mm. Some pumps, including Elvie, offer half sizes or inserts, so check what's available.

Remember that your left and right nipples can be different sizes. Measure both and choose a flange for each side. Many women overlook this and end up with one side that doesn't fit well.

After you start pumping, assess the fit. Your nipple should move freely without touching the sides of the tunnel. If it rubs, go up a size. If you see excessive areola being pulled in, go down. This trial-and-error is normal and part of the process.

• Measure both sides—difference of 1 mm or more is common.
• If you're between sizes, start with the larger one to prevent pinching.

Using a sizing tool vs. manual measuring

A printed sizing tool can simplify the process. These tools often feature circles or slots that you hold over your nipple to visually match your size. They're quick but can be less precise if you're not careful about placement.

If you're using an Elvie pump, you can also look for a sizing tool that's specifically designed for their flange system. For example, the Breast Pump Sizing Kit includes a sizing tool that helps you identify the correct insert size, making it easier to test different options before you buy more flanges.

Manual measuring with a tape or ruler is accurate if done correctly, but a sizing tool can reduce the chance of error. It's often a good idea to do both and compare results.

• Hold the sizing tool flat against your nipple, not at an angle.
• If the tool says two different sizes, try both with your pump to see which feels better.

How a breast pump sizing kit helps

A breast pump sizing kit typically includes multiple insert sizes that you can try with your pump. This takes the guesswork out of choosing a size. You can pump each size for a few minutes and see which one feels comfortable and produces the most milk.

The Breast Pump Sizing Kit by Elvie is designed to work with Elvie Pump and includes five different insert sets to help you find a comfortable fit. It also comes with a sizing tool and a Pump Sizing 101 guide, making it a helpful resource for first-time pumpers or those switching to a wearable pump.

One advantage of inserts is that they let you adjust the size without buying a new flange each time. If your size changes, you can simply swap the insert. This can be more cost-effective than purchasing multiple flanges.

• When trying inserts, pump for at least 5 minutes to evaluate comfort and output.
• Keep track of which insert gives you the best flow; note that your left and right sides may need different sizes.

Common mistakes and troubleshooting

One common mistake is measuring only once, right after nursing when the nipple is fuller. This can lead to a size that's too large. Always measure at least twice on different days to ensure consistency.

Another error is ignoring the symptoms of a wrong size. If you experience persistent pain, reduced output, or nipple trauma, don't assume it's normal. Re-measure and adjust your flange size.

If you're between sizes, try both. Sometimes the larger size feels more comfortable but doesn't empty as well, while the smaller size may be more efficient but less comfortable. Finding the balance is key.

• If you notice a decrease in milk output, check your flange size first before changing your pumping schedule.
• Remember that your flange size can change during the first few months postpartum; re-measure regularly.

Steps to measure your flange size at home

1. Measure nipple diameter: Use a soft tape or ruler to measure the diameter of your nipple at the base, in millimeters. Measure both sides. Common mistake: including the areola. Checkpoint: your measurement should match the width of your nipple only.
2. Add 1–3 mm for comfort: Add 1 to 3 mm to your nipple diameter to allow for free movement. This is your estimated flange size. If between sizes, start with the larger one to avoid pinching.
3. Use a sizing tool for confirmation: Hold a printed sizing tool over your nipple to cross-check your manual measurement. This helps reduce error. If the tool shows a different size, try both with your pump to see which feels best.
4. Test with inserts or flanges: If you have a sizing kit, pump with different insert sizes for a few minutes each. Evaluate comfort and milk output. Checkpoint: your nipple should move freely without rubbing; output should be consistent.
5. Re-measure regularly: Your flange size can change over time, so re-measure every few months or if you notice discomfort or reduced output. If you experience pain or decreased milk, revisit your size before troubleshooting other causes.

Products to help with sizing

• Breast Pump Sizing Kit: 5 Insert Sets for Inclusive Sizing, Sizing Tool to easily find your size, Pump Sizing 101 guide, support via Sizing Specialist. This kit includes multiple insert sizes so you can test different fits without buying multiple flanges, helping you find the most comfortable and efficient size for your Elvie Pump.
• Elvie Pump and Elvie Catch: Elvie Pump is an ultra-quiet, slimline wearable electric breast pump (5oz) with Smart Rhythms TM to boost milk flow; Elvie Catch is a pair of silicone milk collection cups (1 oz) to catch every drop. When you find your correct flange size, an Elvie Pump ensures efficient expression, while Elvie Catch can capture any letdown leaks, maximizing your milk collection.

Finding the right breast pump flange size doesn't have to be a guessing game. By measuring accurately, using a sizing tool, and testing with a breast pump sizing kit, you can ensure a comfortable and efficient pumping experience. Remember to re-measure periodically and trust your body's signals—if something feels off, adjust and try again.