Breast pump flange sizing guide
By The Zomee Team · Updated September 25, 2026
To find your flange size, measure the widest part of the tip of your nipple in millimeters, match that number to the closest size in the charts below, then confirm the fit by how pumping feels. The whole check takes a few minutes.
If none of the sizes included with your pump fits, our Perfect Fit Promise™ sends you a pair in the size you need at no extra cost. It covers flanges from 15 mm to 32 mm and soft silicone inserts from 13 mm to 21 mm. The Mom Line™ can help you measure.
The goal of every session is to remove milk frequently and completely
The right breast shield fit is what makes that possible. With a correct fit, milk typically starts flowing within about 15–20 seconds.
15–20 sectypical time for milk to start flowing with a correct fit
What is a breast pump flange, and what does it do?
A breast pump flange is the funnel-shaped part of the pump that fits over your nipple and breast, creating a seal and guiding milk into the milk collector. Its size refers to the diameter of the tunnel your nipple sits in, not the outer rim.
One common mix-up: flange size is not the wide outer part you can see from across the room. It is the tunnel, the narrower opening your nipple sits in while you pump. That is the number we are solving for.
What is the difference between a flange and a breast shield?
They are the same part. Flange and breast shield are two names for it, and Zomee uses one or the other depending on the pump.
Flanges
The name we use on tabletop pumps.
- Zomee Z1 and Z2 double electric pumps
- Mother's Nature™ H1 dual-motor pump
Flanges are sold as a pair, so the product names are plural.
Breast shields
The name we use on wearable and hands-free pumps.
- Mother's Nature W1 warming wearable pump
- Zomee Fit wearable pump
- Hands-Free Collection Cups
Breast shields are sold one at a time.
If you are between flange sizes, or the fit is still not quite right, an insert can get you there without buying a whole new part. Inserts are soft, BPA-free silicone pieces that sit inside your breast shield or flange and reduce the tunnel size for a more precise fit.
| Product line | Sizes available | Works with |
|---|---|---|
| Flanges | 15, 17, 19, 21, 24, 28, and 32 mm | Z1, Z2, and H1 kits |
| Breast shield inserts | 13, 15, 17, 19, 21, and 24 mm | Z1, Z2, Fit, Hands-Free Collection Cups, and W1 (not the H1) |
| Mother's Nature shields | 19, 21, and 24 mm | H1, Z1, and Z2 kits |
Why the right size matters
A flange that is too small can restrict your nipple and cause rubbing or pinching; one that is too large can pull in too much breast tissue. Either way, a poor fit can prevent a proper seal and affect how much milk you are able to express.
Too small, and your nipple does not have room to move the way it wants to. Pumping starts to feel tight and effortful, and you may notice that you are not emptying fully. Too big, and the flange pulls in more breast tissue than it should, which brings its own kind of discomfort and can get in the way of a good session.
Neither one is something to push through. A flange that does not fit cannot form a proper seal, and that affects both your comfort and how much milk comes out. If something feels off session after session, trust that feeling and try a different size.
Flange size is also the first thing to check on a pump that seems weak. Incorrect flange size is one of the most common causes of low or no suction that The Mom Line hears about, and the most common reason a brand-new pump seems to have none at all.
Measure
How to measure your nipple for flange size
All you need is a millimeter ruler. The W1, H1, and Zomee Fit include a nipple ruler, and the printable one below works too.
- 1Prepare the nippleGently place your thumb and index finger on the nipple for 15–20 seconds until it naturally perks up. Do not squeeze or apply pressure.
- 2Measure the tip of the nippleMeasure the widest part of the tip of the nipple with a ruler, in millimeters. Do not include the base of the nipple or the areola, and measure each side separately.Zomee measures from the top (tip) of the nipple, not the base. This gives a more accurate measurement for finding your best-fitting flange, breast shield, or insert size.
- 3Select your starting sizeYour starting size is the measurement of the tip of the nipple in millimeters, matched to the closest breast shield or insert size. There is nothing to add to it.
- 4Adjust for comfortMeasuring is only a starting point. Try several breast shield sizes to find the one that gives you the best comfort and milk flow.
The ruler
Print a nipple measuring ruler
You can measure today, even if your pump has not arrived. Print the nipple ruler below on any printer, check the scale, and you will have your measurement in a few minutes.
The printed ruler includes sizing circles, a millimeter scale, and a scale-check bar, because printers and browsers like to shrink pages to fit. A shrunken ruler skews every measurement, so confirm the scale before you trust it.
- Print the ruler at 100 percent, sometimes labeled actual size, with fit-to-page scaling turned off.
- Hold a standard bank card against the check bar; the two should match exactly in width. If they do not, reprint at 100 percent before measuring.
- Measure the widest part of the tip of your nipple, not the base or the areola, using the circles or the millimeter scale, and measure both sides.
- Match each measurement to the size charts on this page, and ask The Mom Line if you land between sizes.
Match
Selecting your starting size
The widest point near the top of your nipple is usually the best starting point for choosing your breast shield size. Your measurement in millimeters maps directly to your starting size, with no need to add anything to it.
During pumping, your nipple responds to the pump's compression, undulating motion, and release, a rhythm designed to mimic a baby's natural suck and release at the breast. Nipple size typically does not change drastically during pumping, so the widest point near the top gives the most consistent guide for choosing a size.
This holds true across all sizes. Most important: if you are not getting milk sprays at all, try another size. If that does not help, The Mom Line can walk you through finding your correct size.
General sizing chart for flanges and breast shields
Match your nipple tip measurement in millimeters to the closest breast shield or insert size below, then confirm it with the feel check further down. If your number sits exactly between two sizes, start with the smaller one and keep the larger one as the next to try.
| Nipple tip diameter | Recommended size | Other sizes to try |
|---|---|---|
| 14 mm or under | 13 mm | 15 mm |
| 15–16 mm | 15 mm | 13 mm or 17 mm |
| 17–18 mm | 17 mm | 15 mm or 19 mm |
| 19–20 mm | 19 mm | 17 mm or 21 mm |
| 21–22 mm | 21 mm | 19 mm or 24 mm |
| 23–26 mm | 24 mm | 21 mm or 28 mm |
| 27–30 mm | 28 mm | 24 mm or 32 mm |
| 31 mm or over | 32 mm | 28 mm |
Mother's Nature flange sizing chart
The Mother's Nature flanges were designed to mimic how a baby's tongue undulates, or waves, on the breast instead of simply sucking, for a more natural way of moving milk. Because the flange combines silicone with a rigid plastic support bridge, it gives the tunnel a firmer foundation than an all-silicone flange. The plastic reinforcement helps stabilize the tunnel while keeping the comfort and flexibility of silicone.
Pro tips
- With the Mother's Nature silicone flange, apply a small amount of lubricant inside the tunnel to help the nipple glide.
- If the flange is too large, it may pull in excess breast tissue, which can cause discomfort and make pumping less efficient.
- If the flange is too small, the nipple may not move freely through the tunnel. It can feel tight or restrictive, and output may be affected.
| Nipple tip diameter | Recommended flange size | Other sizes to try |
|---|---|---|
| 20 mm or under | 19 mm | 21 mm |
| 21–22 mm | 21 mm | 19 mm or 24 mm |
| 23 mm or over | 24 mm | 21 mm |
Mother's Nature flanges come in 19, 21, and 24 mm. If you measure under 19 mm or over 24 mm, Zomee flanges run from 15 mm to 32 mm and fit the same H1, Z1, and Z2 kits.
Confirm by feel
Signs of a correct flange fit
Breast shield sizing is not an exact science. The way your nipple looks inside the tunnel is not necessarily an accurate indicator of fit, because the nipple naturally elongates and compresses during pumping, just as it does during breastfeeding.
Pay attention to the tip of your nipple instead. It should feel comfortable and move freely, without rubbing, pinching, or pulling.
Too small
Rubbing, pinching, and soreness that lingers after pumping.
Your nipple is fighting the tunnel walls instead of gliding through them. Afterward it might look swollen, misshapen, or pinched, sometimes with a change in color (white, red, or purple). Feeling like you never fully empty is another sign the tunnel is too small.
Try the next size up
Just right
Light contact, no rubbing, a gentle back-and-forth glide.
Your nipple lightly grazes the tunnel walls and glides easily, with no rubbing or pinching, as milk starts to spray or flow within about 15–20 seconds. This is what it is supposed to feel like: almost nothing, or a gentle tug. If that is you, you are done.
You have found your size
Too big
Discomfort, less output, more dripping than spraying.
Sessions run longer, output feels lower, and you are getting more of a drip than a spray. Your nipple might be moving around too much in the tunnel, or the flange may be pulling in more areola than it should, sometimes with swelling or a dull ache.
Try the next size down
By pump
Which sizes does each pump include?
Every Zomee pump includes at least two sizes.
If you are still deciding which pump is yours, answer three questions in the pump quiz and we will find your match; the sizing method here works the same on all four.
| Pump | Included | More sizes |
|---|---|---|
| Mother's Nature™ W1 Warming Wearable Breast Pump | Five sizes: 24 mm warming breast shields and 15, 17, 19, and 21 mm inserts, plus a nipple ruler | Flanges from 15 mm to 32 mm and inserts from 13 mm to 21 mm come free through our Perfect Fit Promise™. |
| Mother's Nature™ H1 Hospital-Grade, Dual-Motor Breast Pump | Two sizes: 19 and 21 mm Mother's Nature breast shields, plus a nipple ruler | Flanges from 15 mm to 32 mm come free through our Perfect Fit Promise™, and the H1 also works with the Zomee Z2 Breast Shield Kit, which runs from 15 mm to 32 mm. |
| Zomee Z2 Pump & Hands-Free Collection Cups Bundle | Four sizes: 17, 19, 21, and 24 mm flanges. The collection cups include three sizes: 24 mm breast shields and 19 and 21 mm inserts | Flanges from 15 mm to 32 mm and inserts from 13 mm to 21 mm come free through our Perfect Fit Promise™. The Zomee Z2 Breast Shield Kit runs from 15 mm to 32 mm. |
| Zomee Z2 Shabbat Mode™ Edition with Hands-Free Collection Cups | Four sizes: 17, 19, 21, and 24 mm flanges. The collection cups include three sizes: 24 mm breast shields and 19 and 21 mm inserts | Same as the Z2. |
| Zomee Fit Hands-Free Wearable Breast Pump | Three sizes: 25 mm breast shields and 17 and 21 mm inserts, plus a nipple ruler and guide | Flanges from 15 mm to 32 mm and inserts from 13 mm to 21 mm come free through our Perfect Fit Promise™. The shop also sells Universal Inserts from 13 mm to 24 mm and the Zomee Fit Breast Shield Kit. |
Perfect Fit Promise™
Sizing comes with a guarantee. If the breast shields included with your Zomee pump are not your size, we send you a pair in the size you need at no extra cost. The promise comes with every Zomee pump.
There are two ways to use it. Fill out the request form at support.zomee.com/flanges-registration, or contact The Mom Line, where real moms and certified lactation consultants help you measure, confirm your size, and submit the request for you.
Good to know
Sizing questions, answered
Should I add a few millimeters to my measurement?
No. Match your tip measurement to the closest size, with nothing added. If another guide had you measure at the base of the nipple, measure again at the tip before you use our charts.
What if I'm between two sizes?
Go with the closest size. If you measure exactly halfway, such as 20 mm, start with the smaller size, 19 mm. If it rubs or pinches, try the next size up.
Do I need a different flange size for each breast?
Sometimes. It's common for one breast to need a different size, so measure both. You can pump with a different size on each side.
Does flange size change over time?
It can, over months of pumping and between pregnancies. Measure again with each baby, and any time a size that fit before starts to rub, pinch, or pull.
Is pumping supposed to hurt?
No, you should never feel pain while pumping. If it hurts, check your flange size and lower the suction. If the pain continues after a size change, call your healthcare provider.
Why does my pump have weak suction?
On a brand-new pump, it's usually flange size. If a pump that worked well loses suction, worn parts are the most common cause. Replace the duckbill valves and diaphragms every 1 to 3 months, depending on how often you pump and how you clean them. On the Mother's Nature™ W1, replace the diaphragms every 2 to 3 months.
Still have a sizing question?
Real moms and CLCs answer your pump, sizing, and parts questions on The Mom Line™.
We take calls 9 AM to 5 PM ET, Monday to Friday. Email info@zomee.com any time.