Your Pump Came With a 24mm. Here's Why That Might Not Be Your Size.

You unboxed your pump, washed every little part, and put it together exactly the way the instructions said. Somewhere in that box was a flange, probably a 24mm. And nobody mentioned that it might not be your size.

Here's the thing: most pumps ship with one standard flange size, often 24mm. It's a starting point, not an answer. Nipples come in all different sizes, and a flange that fits one person perfectly can feel completely wrong on someone else.

So if pumping has felt uncomfortable, or just a little off, it's not you. It's a gap in what we're all taught. Most of us were never told that flange size is something you're supposed to check, let alone how to measure it.

Let's fix that.

When you pump, your nipple moves back and forth inside the flange tunnel, the narrow part of the flange. That tunnel needs to give your nipple enough room to move freely, without so much room that other tissue gets pulled in along with it.

When the fit is off in either direction, things get crowded. A tunnel that's too big can draw in areola tissue, and a tunnel that's too small can squeeze the nipple itself. Either way, that crowding can be uncomfortable, and it can make it harder for milk to flow out the way it's meant to.

One clue to watch for: seeing drips of milk instead of sprays while you pump. It's not the only sign, and it doesn't mean anything is wrong with you or your body. It's just one way your pump might be telling you the fit could be better.

The goal here is simple: a fit that feels comfortable for the whole session, and in between sessions, too.

Here's how each one tends to feel, in plain terms.

Too big

• "It hurts, or at least it's uncomfortable."

• "A lot of my areola gets pulled into the tunnel."

• "I can't keep the flange suctioned to my breast while the pump is on."

• "I'm seeing drips instead of sprays."

• "I still feel full after I'm done."

• Pumping sessions lasting a long time (average is 15-20 min)

Too small

• "My nipple feels stuck, like it can't move inside the tunnel."

• "It pinches, or I get a sharp pain."

• "My nipple looks white or pale afterward, or it burns or itches between sessions."

• "My nipples are cracked or sore."

Just right

• "It's comfortable the whole session, and after."

• "My nipple moves freely and touches the sides of the tunnel without pinching."

• "Very little of my areola gets pulled in."

• "I see sprays of milk while I pump."

• Pumping sessions feel more efficient

Recognize yourself in the first two lists? That's useful information, not a failure. It just means it's time to measure.

You'll need a nipple ruler (the Silicone Nipple Ruler works great), a mirror, and about five minutes.

Step 1: Measure the nipple tip only

Measure the width of your nipple tip, not the areola (the darker area around it). The areola doesn't factor into flange size, so leave it out of the measurement.

Step 2: Measure each side separately

Your two nipples may not be the same size, and that's completely normal. Measure each one on its own, and write both numbers down.

Step 3: Measure before you pump

Take your measurement before a pumping session, not right after.

Step 4: Try the sizes on either side while pumping

Your measurement is a starting point. From there, try the size closest to it, then the sizes just above and below, while you're actually pumping. Pick the one that feels the most comfortable. It's normal to land on a different size for each side.

A few measuring tips

• Use a mirror. It's a lot easier to see what you're doing. You can also snap a photo to double-check your measurement.

• Hold the ruler flat. Bending it can throw off the number.

• Two ways to measure. Our Silicone Nipple Ruler has a millimeter edge for the most precise reading, plus cut-out circles you can fit over your nipple tip.

• Flat or inverted nipples? Gentle stimulation can help bring the nipple out for measuring. If it doesn't, that's okay. You can still measure.

Here's something else nobody mentions: the size that fits today might not be the size that fits a few months from now. Breasts can change throughout pregnancy and your whole feeding journey.

There's no set schedule for when that happens, and no rule about which way it goes. So instead of watching the calendar, pay attention to how pumping feels. If a fit that used to feel great starts to feel off, you notice any of the too-big or too-small signs above, or you notice a dip in your supply, that's your cue to measure again.

The good news is that once you know how to measure, rechecking takes just a few minutes.

Here's the best part: finding your size doesn't mean replacing your pump or buying a whole new set of flanges. Flange inserts slide right inside the 24mm flange you already have and make the tunnel smaller, so you can try a different size with the pump you know.

What's in the Flange Sizing Kit

Our Flange Sizing Kit was made to take the guesswork out of this whole process. Inside, you'll find:

• A silicone nipple ruler with two ways to measure: a millimeter edge and cut-out circles.

• Five pairs of silicone flange inserts in 13, 15, 17, 19, and 21mm, so you can try the sizes on either side of your measurement while you pump.

• Two QR codes on the box. One links to our in-depth flange sizing guide, and the other to a step-by-step video that walks you through measuring.

The inserts fit most standard 24mm traditional plastic flanges, plus our Silicone Collection Cups. If the insert is not sliding into place, a little Organic Pumping Spray in the flange tunnel can help the insert glide in. And one spray inside the flange insert tunnel can make pumping more comfortable.

Caring for your inserts

• Before first use, sterilize them in a deep, wide pot of boiling water for 3 to 5 minutes, fully submerged and not touching the bottom or sides.

• After that, hand wash in warm, soapy water and rinse well. Skip the dishwasher and any high heat. Cold or UV sterilization is fine.

• Replace them every 3 weeks, depending on how often you pump, and right away if one tears.

Pumping shouldn't hurt. If you've measured, tried a few sizes and it still doesn't feel right, or if you're dealing with nipple pain or damage, please reach out to an IBCLC or lactation consultant. They can look at the full picture, from fit to pump settings to anything else that might be going on.

The Flange Sizing Kit is a fit tool. It's a great place to start, but it's not a substitute for hands-on support from a professional who can see what's happening.

And remember: if your 24mm never felt quite right, that was never on you. Nobody taught us this one. Now you know, and that's worth celebrating.

Keep reading:

• Shop the Flange Sizing Starter Kit

• Silicone Nipple Ruler Instructional Guide