How to Find the Right Flange Size to Pump Comfortably

If pumping hurts, this is almost certainly why.

Flange sizing is the most overlooked and most consequential detail in the entire pumping experience. It is also the most common thing nobody tells you about, not at the hospital, not in the discharge notes, not in the instruction booklet that came with your pump.

Get it right and pumping is comfortable, effective and often almost painless. Get it wrong and pumping can be painful, slow and discouraging and you will likely be blaming yourself or your supply or your pump when the actual problem is a piece of plastic that is 2mm too wide.

This guide tells you everything you need to know about flange sizes what they are, why they matter, how to measure correctly and what to do if you are between sizes.

What is a flange and what does it actually do?

A flange, sometimes called a breast shield, is the funnel-shaped piece of the pump that sits against your breast. Your nipple goes into the narrow tunnel at the center and the wider rim creates a seal against the skin around your areola.

The flange does two things simultaneously. It creates the airtight seal that allows suction to build. And it guides your nipple into the tunnel where the suction can draw milk out effectively.

For both of these functions to work properly the flange needs to fit your nipple correctly. Not your breast. Not your areola. Your nipple specifically.

Why the wrong size causes problems

If the flange is too large:
Too much of your areola gets drawn into the tunnel along with your nipple. This is the most common fitting error. The areola tissue is not designed to be pulled repeatedly and doing so can cause bruising, soreness and reduced blood flow. More practically, it reduces the efficiency of milk expression because the suction is not being applied in the right place.

If the flange is too small:
Your nipple presses against the sides or the tip of the tunnel. This causes friction which causes pain, cracking and in some cases abrasion. A flange that is too small can also restrict the movement of the nipple which physically impedes milk flow.

In both cases:
Output is lower than it should be, sessions are uncomfortable and many mothers conclude that pumping simply is not working for them when the issue is entirely fixable.

How to measure your nipple correctly

You will need a ruler or a measuring tape marked in millimeters. This takes about two minutes.

Step one: Measure the diameter of your nipple at its base, the widest point where the nipple meets the areola. Do not include the areola itself in this measurement. You want the nipple only.

Step two: Write down that measurement in millimeters.

Step three: Add 2 to 3mm to your measurement. This is your starting flange size.

The 2 to 3mm gap between your nipple diameter and the flange tunnel diameter allows your nipple to move freely during suction without touching the sides. This free movement is what allows effective milk expression without friction or pain.

Example: If your nipple diameter measures 18mm, your flange size should be 20mm or 21mm.

A note on timing

Nipple size changes during pregnancy and in the early postpartum weeks as your body adjusts to feeding and pumping. Most lactation consultants recommend measuring once breastfeeding and pumping are established, usually around two to four weeks postpartum, rather than before your baby arrives.

It is also worth remeasuring if you experience a sudden change in pumping comfort or output after a period of things working well. Nipple tissue can change with regular pumping and a size that fit perfectly at six weeks may not fit as well at four months.

Understanding the standard sizes

Most breast pump flange sizes range from 15mm to 36mm. The most commonly used sizes fall between 17mm and 24mm which covers the majority of women.

The Solyymoms Air 1 comes with four sizes in the box- 17mm, 19mm, 21mm and 24mm because we know that most women fall within this range and we did not want anyone to have to buy additional sizes separately. If your measurement suggests a different size please contact us before ordering and we will advise.

As a general reference:

• 17mm: Nipple diameter of approximately 14 to 15mm
• 19mm: Nipple diameter of approximately 16 to 17mm
• 21mm: Nipple diameter of approximately 18 to 19mm
• 24mm: Nipple diameter of approximately 21 to 22mm

These are starting points. Your actual experience in the first one or two sessions will tell you whether you have the right fit.

How to check whether your flange fits correctly

Once you have assembled your pump and begun a session, watch what happens to your nipple during suction:

Signs of a good fit:

• Your nipple moves freely in and out of the tunnel during suction cycles without touching the sides
• Little or no areola tissue is being drawn into the tunnel, a very small amount of areola movement is normal and acceptable
• The session is comfortable, you may feel pressure and fullness but not pain or sharp sensation
• Milk flows steadily once letdown occurs

Signs the flange is too large:

• More than a few millimeters of areola is being pulled into the tunnel
• The suction feels diffuse rather than focused
• You notice redness or a ring-shaped mark on your areola after the session
• Output is lower than expected despite letdown occurring

Signs the flange is too small:

• Your nipple appears compressed or is rubbing against the tunnel walls
• You feel a squeezing or pinching sensation during suction
• There is redness or marks on the nipple itself after the session
• The session is painful

What to do if you are between sizes

This is more common than most pump brands acknowledge. If your measurement suggests you fall exactly between two standard sizes here is how to approach it:

Start with the larger size. In most cases a slightly larger fit causes fewer problems than a slightly smaller one because the friction issue with too-small flanges tends to manifest as pain very quickly while a slightly too-large fit may simply mean slightly lower efficiency rather than discomfort.

Try three sessions with the larger size. If you notice significant areola being drawn in or bruising, try the smaller size. If the smaller size causes friction or pain, go back to the larger.

Some mothers find that one size works on one side and a different size on the other. This is completely normal, breasts and nipples are not identical. Using a different flange on each side is entirely fine and more common than you might think.

The difference good flange fit makes in practice

We hear versions of this story constantly from our community.

A mother contacts us because her pump is not working well, low output, discomfort or both. She has been using the pump for two weeks and is thinking of giving up. We ask about her flange size. She tells us she is using whichever size came in the box without measuring. We walk her through the measurement process. She was using a 24mm flange with a 15mm nipple, nearly 10mm too large.

She switches to the 17mm. Within two sessions: significantly improved output, no pain, no frustration. Same pump. Same mother. Different piece of silicone.

This scenario is so common it is the first thing we check when a customer contacts us with pumping problems.

Replacing your flanges over time

Silicone flanges are consumable parts. With daily use the silicone will eventually lose some of its softness and the material may show minor wear. Most lactation consultants recommend replacing flanges every two to three months with daily use.

Signs that your flange may need replacing:

• The silicone has stiffened noticeably
• There are visible cracks or tears
• You have noticed a gradual reduction in suction quality despite everything else being correctly assembled
• Pumping has become less comfortable than it was in the early weeks

Replacement flanges and parts are available directly from us. If you are not sure whether it is time to replace, message us on WhatsApp and we can help you assess.

A note for mothers with larger or smaller nipples

Standard pump flange ranges do not work for every mother and this is a real problem that the pumping industry has been slow to address.

If your nipple diameter measures below 13mm or above 23mm you may find that standard sizes are not comfortable. This is not a failing on your part. It simply means you need a size outside the standard range.

If you are in this situation please contact us before ordering. We can advise on the best approach for your specific measurements and ensure you are not purchasing equipment that will not fit correctly.

The one thing to do before your first pumping session

Measure your nipple. Do it now, before you assemble the pump, before you sit down for your first session. It takes two minutes and it may be the single most useful two minutes you spend in your entire pumping journey.

If you are not sure how to measure or are not confident in your reading, message us on WhatsApp with your measurement and we will confirm the right size for you. This is a service we offer to every customer before and after purchase because getting this right is that important.

Summary: the quick reference

All four sizes - 17mm, 19mm, 21mm and 24mm are included in every Solyymoms Air 1 box. You can try different sizes in your first few sessions without any additional cost.

Still not sure about sizing? Message us on WhatsApp before you order. We have helped hundreds of mothers find the right fit and we are happy to help you too.