Finding Your Breast Pump Flange Size

Maybe pumping breast milk isn’t going as well as you hoped. You may not be getting as much as you expected. Or maybe your nipples are sore. What gives? The flange size you’re using could be the problem.

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The flange size is the width of the tunnel that your nipple goes into. But one size doesn’t fit all — or even most — when it comes to flanges.

“Everyone’s body is different. And it’s common for nipples to stretch or change shape while breastfeeding or pumping,” explains pediatrician and breastfeeding medicine specialist Heidi Szugye, DO, IBCLC. “That’s why it’s important to check the fit often and adjust if needed.”

Finding the right fit might feel like rocket science amid postpartum brain fog. But Dr. Szugye breaks down the steps and what a well-fitting flange looks and feels like.

How to measure your flange size

How to find the right breatfeeding flange fit

The flange (breast shield) is the cone-shaped cup that looks a bit like a small megaphone. The flange part rests on your areola and breast. The tunnel is where your nipple moves in and out. “A proper flange fit makes pumping comfortable, prevents nipple trauma or swelling, and allows for effective milk removal,” Dr. Szugye says.

Almost all flange tunnel sizes are measured and labeled in millimeters (mm). Sizes range from 13 mm to over 30 mm. Many breast pumps come with a standard “medium” size (usually around 24 mm). But this doesn’t fit everyone.

The right flange size mainly depends on the size (width) of the base of your nipples.

If you’re still pregnant and eager to know your size, it may be best to wait until after birth. “Hormones can change your nipple size throughout pregnancy and after birth,” she adds. “Measuring too early may lead to frustration later when it’s time to pump. But it can give you a general ballpark.”

A lactation consultant or breastfeeding medicine specialist can help you through the measuring process. Or you can do it at home following these steps.

1. Stimulate your nipple

Using your pointer finger and thumb, gently roll your nipple for a few seconds to stimulate it. Think of your nipple as a radio dial. Do this before pumping or nursing when your nipples are in a “neutral” state.

2. Measure your nipple

Use a measuring tape or a printable measuring ruler to find the width (diameter) of your nipple. If your breast pump brand has a printable ruler, it may help to use that.

Measure your nipple in millimeters at the widest part. This is typically the base of your nipple. Don’t measure your areola — the darkened tissue around your nipple.

Measure both nipples, as they may be different sizes.

3. Choose your size

So, now you have your nipple measurement. That’s it, right? Not quite.

“Most women find that adding 2 to 4 mm to their nipple size provides the most comfortable and effective flange size,” Dr. Szugye explains. “But there’s no evidence-based tried and true formula — this just gives you a starting point. Like shoes, sometimes, you have to try different sizes and see what works best.”

For example, if your nipple is 18 mm, it may fit best in a 20 mm or 21 mm flange. But for some, 18 mm may also work.

On top of that, flanges typically increase in 3 to 4 mm increments (for example, from 21 mm to 24 mm). So, you may need an insert that goes into a bigger flange to create the best fit.

If this math has you confused, reach out to your provider or a lactation consultant for help.

Signs of a good flange fit

You may be wondering what a good flange fit looks and feels like. Especially when your nipple may act or look differently under a pump’s suction.

A good fit means:

Your nipple moves freely in the flange tunnel.
You don’t feel pain or discomfort while pumping.
You’re able to express milk effectively.
Your nipple doesn’t look swollen and larger after pumping. (But it may look longer if you naturally have flat or inverted nipples.)
There’s no cracking, bruising or bleeding after pumping.

Here are some tips for getting the best fit:

Always center your nipple in the flange before you start pumping.
Check the fit while pumping using your usual vacuum setting in expression mode.
If you’re between sizes or still uncomfortable, try a different style. You may find better comfort using different materials, like silicone instead of plastic. Flange shapes can make a difference, too, like tapered or oval.
If a different style doesn’t help, you may need to adjust the suction or the amount of time you spend pumping.

Signs of an incorrect flange size

The main signs that your current flange size isn’t right for you are pain and less milk output than expected. The specific signs vary a bit depending on whether the flange is too small or too big for you.

Signs your flange is too small

If your current flange is too small, you may:

Feel pain or tenderness in your nipple
See that your nipples don’t move in the tunnel
Have nipple trauma (like cracks and blisters)
Have little milk output
Have purple nipples or have a pale ring around the nipple base

Signs your flange is too big

If your current flange is too big, you may:

See your areola (the dark skin around your nipple) getting pulled into the tunnel
Feel pain or a tugging sensation
See gaps between your breast and the flange
Not have much milk coming out, even after increasing suction
Have a discolored or sore ring around your areola
Have nipple and areolar swelling after pumping

What to do in the meantime

It may take a few days to receive the correct flange size if you’ve ordered it online. To try to save your nipples while you wait, you can care for them in these ways:

Apply a nipple balm that doesn’t contain lanolin.
Apply MediHoney®, a special medical formula with sterilized honey.
Use warm compresses and/or hydrogel nipple pads.

If the thought of using your breast pump has you wincing, consider hand-expressing breast milk. You likely won’t get as much milk out. But it can give your nipples a rest until you get your new flange.

Hang in there

Pumping is a lot of work. It’s OK to feel frustrated — the wrong flange size can cause irritation in more ways than one. The good news is that the proper size can make a world of difference.

“Any breast milk is beneficial to your baby,” Dr. Szugye reinforces. “Try to take it one session at a time and get support.”