How do I find the right flange size?

The short answer

👍 Getting the ‘right’ flange size can make a big difference to your comfort and milk flow.

😟 But it can be confusing figuring out which flange size is ‘right’

📏 You could start by measuring your nipple with a ruler, or our handy ‘nipple-sizer’ printout

👩‍⚕️ Ask your lactation consultant for help, especially if you’re having pain or discomfort 

Don't want to read on? Download the nipple ruler and flange-fit checklist by clicking on the image 👇🏽

nipple ruler and flange-fit checklist download 1-pager

What is a flange?

Most pumps come with different sized flanges, which are the cone-shaped parts that fit to your breast. 

What is flange size?

When people talk about “flange size”, they are referring to the diameter of the tunnel that your nipple is sucked into. 

diagram of a breast pump showing the flange (the cone your breast goes into), and the diameter of the tunnel (the part that connects the flange to the rest of the pump)

What is the usual flange size?

Breast pumps tend to have a range of flange sizes from about 20 millimetres to 36 millimetres. 

If you don’t specifically order a different flange size, you’ll probably receive their standard size when you get your pump, which is usually about 24/25mm. Some pump brands come with two standard sizes to save you the trouble of ordering more than one. 

Here’s a table of all the flange sizes that are available for pump brands.

flange size table

Please let us know if you can’t see your pump, or we’ve got it wrong, and we’ll get onto that ASAP. 

Finding the correct size

It’s important to get the right flange size for you, so that you have the best possible comfort, seal and milk flow. 

If your pump flange size is too big, you can pull your areola unnecessarily into the pump funnel and damage the skin and tissue. We know from this study, and this study, that about 15-17% of women who use breast pumps have nipple injury and damage.  

If your pump flange size is too small, you can rub your nipple against the plastic or block milk duct openings. 

 A gif showing a pump flange that is too large. The nipple is drawn in, but the areola is also, leaving it swollen and sore.

👆🏼 This flange is too large. See how the areola is sucked in with the nipple and swells. 

gif showing flange that is too small. The nipple rubs along the side of the flange and can't extend properly.

👆🏼 This flange is too small. See how the nipple rubs on the side of the tunnel, and can’t really move much. 


👆🏼 This flange looks about right. See how the nipple extends within the tunnel, but the areola says mostly where it is.

Unfortunately, the only thing you can change with most breast pumps to suit your nipple is the diameter of the tunnel that your nipple is sucked into. 

Pumps don’t really take into account your nipple shape (inverted, flatter, rounder, longer), or how your nipple responds to the pump suction – whether it is elastic (stretches a lot) or fibrous (doesn’t stretch much). We made Milkdrop cushions for this reason, but more on that later. 

Shop milkdrop breast pump cushions for a comfier pump

How do I know if my flange size is too small? 

Some signs that might indicate that your flange is too small are: 

  • your nipple doesn’t move easily in the tunnel of the flange

  • you have indents on the top or close to the side of the nipple

  • you have pain or rubbing of the nipple (not areola) 

  • you feel like your ducts are blocked by the flange

  • it takes you ages to get milk flowing

  • your breasts still feel full after expressing

How do I know if my flange size is too large? 

Some signs that might indicate that your flange is too large are: 

  • your areola (the part around your nipple) is drawn into the flange

  • you have swelling and soreness of your areola and the base of your nipple when you take the pump off 

  • you have chafed skin in a ring around your areola

  • you don’t have good suction - the pump falls off, loses contact with your breast when its on, or it makes suction-y squelchy noises

  • you have milk leaking from the pump between your breast and the flange

  • it takes you ages to get milk flowing

  • your breasts still feel full after expressing

How will I know if I have a proper flange fit? 

When you have the right size for you, you should be able to check-off this list. 

image of a checklist (written below)

So, your nipple should move freely, without touching the sides. Your areola should move a tiny bit, but not be sucked into the tunnel with your nipple. You may feel tugging but not pain or discomfort. When you remove your breast after a session, your nipple might be extended but your areola shouldn't be bloated and sore. You should have a good seal, which means you won't have air around your nipple or hear any suction-y noises 🤭. You should get good milk flow (squirts or faster droplets of milk), and after pumping for a session, you should feel that you've drained as much milk as you can. 

If you find yourself needing icepacks, or heatpacks when you’re finished, then check your flange size, and seek help from your lactation consultant or doctor. 

How do I choose the right flange size for my nipple?

To choose the right flange size, the most common approach is to measure your nipple diameter and choose the closest flange available for your pump. 

Scroll down for detailed instructions on how to measure your nipple. 

Measuring can be confusing because your nipple is affected by whether you’ve just pumped (and your nipple is swollen) or not. Also, sometimes you are between sizes or your nipple is much smaller than what’s available.

If you’re having trouble measuring, but you have access to a few different flange sizes (perhaps your friendly lactation consultant or some friends who pump can help you here), then you can go by feel. Just try on different flanges, and work through the flange-fit checklist above.

Whichever method you try, remember that the flange size you choose is just a starting point. You may need to change it up as you get used to pumping or as your breast changes over time.

How do I measure my nipple?

Here are the steps to measuring your nipple. Much like cooking a recipe, you’ll have the most success if you read through the steps first (even though it’s boring). 

Step 1. Get yourself some sort of measuring device. 

You can use a ruler, some measuring tape from a sewing set or a special ruler designed especially to figure out nipple size, which you can download here. 

series of semi circles increasing in nipple size

👆🏼 If you use this fancy nipple ruler, you need to print (make sure your printer isn’t scaling the document in the settings) and cut out the semi-circles with scissors. 

Step 2. Look at your nipple (we’re not kidding)

You need to figure out what you’re measuring exactly, before you start. 

You want to measure the distance from one side of your nipple to the other. Your nipple is the pointy or bumpier part in the middle. Your areola is the wider circle or darker skin around it👇🏽

 diagram of a breast and areola and nipple, showing the nipple measurement

To measure, you will start from one side of your nipple where it meets the areola, and measure across to the other side. Take care not to measure the areola, because you’ll end up measuring too big.  

👇🏽 Here’s what that might look like on your nipple. photo of a lactating nipple with nipple measurement markedphoto of a lactating nipple with nipple measurement marked

Step 3. Prepare your nipple. 

Some advice recommends that you measure after pumping, but that can be problematic for two reasons:

  1. You have to have a pump handy, and be ready to use it (i.e. lactating right now)

  2. If you’re pumping on a flange that’s too large already, your nipple will likely swell to the size of the flange and be bloated. This would mean that you’d measure too large. 

We suggest that rather than pumping, just stimulate your nipple. You can do this by pulling on your nipple gently with your fingers, which will raise it or plump it up a bit. 

Step 4. Measure your nipple

Measuring is often best done in front of a mirror, or with the help of your partner or carer. 

Using the special nipple ruler: 

Place the semi-circle cut-outs against your nipple, starting with the smallest one. Keep going up a size until your nipple comfortably pokes through. If you have inverted or flatter nipples, choose the size that fits around your nipple. 

 series of semi circles increasing in nipple size

👆🏼 click this to download the nipple ruler. 

Using a regular ruler or measuring tape: 

If you’re rusty on reading millimetres and centimetres on a ruler, here’s a refresher. 

 ruler annotated with 1cm and 10mm

👆🏼The little lines are millimetres (mm). Most rulers show a big line every 10mm, and a half line every 5mm. As for centimeters? Well, 10mm = 1cm!

image of a lactating nipple with a ruler overlain

👆🏼 When you’re measuring, you just need to count every line (the millimetres) from one side of the nipple to the other to figure out your nipple “size” or diameter. In this photo, the nipple measurement is 17mm. 

Step 5. Do some math

Now you have your diameter, add 1-2mm and choose the closest flange size available from your pump brand. Use the table above, or google your pump for flange sizes. 

You may run into issues here, especially if you measure on the smaller end. For example, if you measure 12mm, you can see that for most brands, then the closest size for you is….21mm. 

Thankfully, there is help for you. The following companies make inserts or separate flanges that you can attach or insert in your pump that better match your size. 

table of after-market flange manufacturers with smaller sizes

Step 6. Test and change it up

As with most things pumping, you may need to try out your new size, run through the flange-fit checklist, and then change if you need. 

Want more?

We've written a whole lot more about finding your perfect flange size, because it's so important for a comfy pump! Check out:

Shop milkdrop breast pump cushions for a comfier pump