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You want the breast pump flange to fit over the nipples and form a vacuum seal around the areola. There should be little or no areolar tissue in the flange tunnel during pumping.

Good fit: Nipple is in the center of the flange. Little or no areola is pulled into the breast pump tunnel

Flange is too big if a portion of areola is pulled into the breast pump tunnel

Flange is too small if the Nipple is pulled to a side of the breast pump tunnel and cannot move freely

Common flange fit questions

Its no exaggeration to say that getting the right flange (quality), and the correct size flange (fit) will save moms everywhere a few tears.

Hopefully this post helps do just that. We will answer a few frequently asked questions including:

  • What are breast shields or breast pump flanges?
  • Why is flange size or flange sizing important?
  • How much areola should be in the flange?
  • What are the different nipple sizes and types?
  • What rules govern flange size or flange sizing?
  • What is nipple sizing and how do I do it?
  • How can I tell if a flange is too big, too small, or the right fit?
  • What should the nipple look like in flanges or breast shield(s)?
  • What is a flange size calculator or a flange size ruler?
  • How can I measure the diameter of my breasts for my flange fit?

What is a Breast Shield or a Breast Pump Flange?

The flange is the funnel-like or cone-shaped part of a breast pump, that is otherwise known as the breast shield. The flange is the part of the breast pump that connects skin-to-skin with the breasts to create a chamber for the pumping extraction of a mother’s breast milk.

The breast pump flange is expected to fit or sit over the nipples and then form a vacuum seal around the areola for breast milk extraction or breast pumping process. The breast pump flange which forms a vacuum seal around your areola, then draws the nipple into its funnel for milk supply.

Flanges come in different sizes and materials to suit the needs, breast types, and comfort levels of breastfeeding mothers. Some of these breast shield materials include plastic, silicone, metal, glass etc.

How much Areola should be in the Flange?

It can be quite hard to find a comfortable milk output pump or decide on the right flange shield that will be suitable for your breasts or nipple size, especially since different sizes and models of breast pumps or breast shields with distinct features and benefits have been made available in the shopping market.

One way of narrowing your choices and making your decision easier is by tracking down the amount of areola in the flange tunnel or breast shield tunnel during the breast milk pumping process.

The areola is the darkened ring of color found around the nipple. The major function of the areola is the stimulation of milk production or let down during milk extraction.

How much areola in flange? It is important to note that little or no areolar tissue is expected to be in the flange tunnel during breast milk pumping. This is advisable to prevent breast-related problems such as crammed milk ducts, breast tissue discoloration, nipple soreness, pain in breasts, swelling, rubbing wound marks, breast cuts, nipple damage, etc.

What are the different nipple sizes and types

When it comes to breastfeeding, the size of the nipple is very important because we can not adequately talk about a nursing mother’s milk production or breast food release without inversely referring to the nipple size.

Based on a medical search, it has been clearly stated that nursing moms and women generally are expected to have nipple sizes that are slightly larger than a quarter of an inch, both in length and width (that is approximately the average size of a ladybug).

Generally, as regards the nipple, there are about eight (8) different types in the world, they are:


They are popularly regarded as protruding nipples. This kind of nipple can be seen to stick out on the areola and face slightly upwards, thereby serving as a good latch-on for a baby.


They are popularly regarded as the flat nipple. This kind of nipple can be seen to have no level variations with the areola, due to the amount of underlying breast tissue present.


They are popularly regarded as the puffy nipple. This kind of nipple can be seen to have an oblong shape that is raised and lies atop the breast mold. For this nip-type, the downward slope flanges are usually a good fit.


They are popularly regarded as the inverted nipple. This kind of nipple can be seen to lie inwards, as the tip area edges into the inner part of the breast.


They are popularly regarded as unilateral inverted nipples. This kind of nipple can be seen to have just one side raised while the other side lies inward.


They are popularly regarded as the bumpy nipple. This kind of nipple can be seen to possess Montgomery glands which are rash-looking “thingy-s” that are sparsely found around the areola. They are also known to occur more in pregnant women.


They are popularly regarded as the supernumerary nipple. This kind of nipple can be seen to have another extra nipple(s) somewhere on the breasts or the body generally.

So, finding the right or correct shield size means having an idea of the different nipple types in existence, and since we’ve touched that bit, let’s move over to the nitty-gritty involved in sizing a nipple.

What is nipple sizing and how do I do it?

Nipple sizing in terms of breastfeeding refers to the measurement of the breast tip or nipple diameter to get the appropriate breast shield or flange size to use while pumping.

And the first rule for nipple sizing is to measure before pumping!

All nursing mothers are expected to measure both of their nipples to determine the best-fitting or proper flange size to use since some might require or need a different flange size for each breast.

To get your correct size and avoid any bit of discomfort, you have to measure first!

So, how then can you size your nipples? What are you to do?

To size your nipple, you could use a metric ruler or a fabric measuring tape from around the house to measure across the base of your nipple where the nipple meets the areola. Please, do not measure the areola to avoid getting the wrong size.

Willow have a handy measure nipple ruler that’s easy to use. They also have an app. I suffer from app download fatigue, so I’d rather use the printable ruler.


The willow nipple ruler helps get the right size flange


After taking the proper measure range, you would notice that the ruler or fabric tape is liberated in centimeters or inches while the flange (breast shield) is in millimeters. At this point, you are to convert into millimeters using the standard Maths rule of 1 cm equals 10 mm.

So, if you measured a nipple size of 3.6 cm in diameter, it would give you a figure of 36 mm after conversion. That is 3.6 × 10 = 36 mm diameter size.

After sizing and measuring, the next step would be to add a number range of 2–4 mm to the actual measurement to help you get the most comfortable pump flange or breast shield to use during breast milk extraction.

This is done to control soreness or discomfort by allowing a small room between your nipple and the flange tunnel, for cases of nipple expansion during milk production or breast milk pumping.

Asides from the metric ruler and the measuring tape, other flange size rulers or measuring tools exist, and some of them include:

Circular Diameter Ruler

This tool makes flange sizing a notch easier as the only effort required is the insertion of the nipple into the provided circle to select the best fit.

Digital Caliper

This can be used to get a more detailed gauge of your flange size as this tool measures the proportion of an object in millimeters.

Flange Size Calculator apps

These tools are digitalized medium that can be used to conveniently measure nipples. They also help to quickly compute breast pump flange sizes and convert measurement across different units.


There are top five (5) flange size charts for breast pump flanges or breast shields, they are:

• < 17mm measurement = 19 to 21mm

• 17 to 21mm measurement = 24mm

• 21 to 25 mm measurement = 26 to 28mm

• 25 to 29 mm measurement = 30 to 32 mm

• 29 to 32 mm measurement = 36 mm

How can I tell if a Breast Pump Flange Size Is the Best Fit?

We spoke with a board certified Lactation Consultant (IBCLC) whose quickest hack to determine the correct breast pump flange size or breast shield size is by feeling fit or comfortable during the pumping process. Here’s a handy acronym : C-O-M-F-Y


The Right Flange is a COMFY flange. Credit: aeroflowbreastpumps

To get the best-fitting flange, here are some signs that indicate a correct breast pump flange size or breast shield size:

•The nipple will be in the center of the flange and would move freely into the breast pump tunnel during milk production.

•The amount of areola tissue that would be pulled into the tunnel will be very little.

•The breast or nipple would not feel sore; during and after breast milk expression.

•The breast would become observably lighter after the breast milk pumping experience.


Read More:

Do I need a nipple shield?


How to tell if your flange size or breast shield size is too big:

•The nipple could become overly inflated, and neither be in the center nor move freely.

•A significantly large amount of areola tissue could be yanked into the breast pump tunnel during milk expression since the flange is too big.

•The nipple could show a whitish coloration, indicating the absence of properly circulating blood flow.

•The quantity of breast milk expressed will be very low.


How to tell if your flange size or breast shield size is too small:

•The nipple could be pulled to the side of the breast pump tunnel during breast milk extraction and not move freely.

•The breast could feel heavy after milk extraction due to an uneven output.

•The nipple may show a reddish coloration.

•You might experience pain in the nipple during and after pumping.

Save your tears for another day

I remember my first-ever breast milk pumping journey. A journey that started when I had no idea what things like breast pump, shield vacuum, or flange meant.

I remember opening the breast pump kit, to see a whole lot of plastic. Breast milk pump parts everywhere. Breast shields (or flanges), nipple tubes, supply tunnels, milk collection bottles, support valves, backflow protector membranes, connectors, and on and on. I know that feeling of confusion only too well.

I have also had to manage breast pain that left me in shambles for a while. Apparently, blindly experimenting with that pump was not the smartest way to go.

Remember, your breast pumping experience and flange sizing journey must always look and feel comfortable. There’s no need to endure pain. Seek help if you need it. Read more tips for making pumping more comfortable here.

How To Make Pumping More Comfortable – 11 Genius Tips