Breast pump flange size guide
Measure your nipple across the base in millimeters, then add 2 to 4 mm. That's your starting flange size. The right fit lets your nipple move freely in the tunnel without pain or areola being pulled in.
Flange size calculator
Measure the base of your nipple, not the areola.
Enter a measurement between 8 and 34 mm. Measure across the base of the nipple only.
No ruler in millimeters? Print our nipple ruler.
Enter your nipple diameter in millimeters to see a starting flange size.
Start with
mm flange
Heads up
A starting point, not a final answer. Measure both sides, since they can differ, and let comfort and how well your breast empties decide.
How to measure your nipple for flange size
- Measure before you pump. Your nipple swells during a session, so a measurement afterwards reads large. Roll it gently between finger and thumb for a few seconds first so it's in its usual shape.
- Measure across the base. Use a ruler in millimeters, or the printable ruler below, straight across the widest part of the nipple where it meets the areola. Leave the areola out.
- Measure both sides. They're often different, and each side can use its own flange.
- Add 2 to 4 mm. That's the starting range the Cleveland Clinic gives. Medela's fitting guide adds 4 mm and picks the closest size.
- Test it with a real session. Pump at your usual suction and check the signs below. The measurement gets you close; how it feels decides.
Print at 100% scale ("Actual size"), not "Fit to page". The preview below isn't to scale on screen.
Nipple sizing ruler
Check the scale first: a credit card is 85.6 mm wide. Lay one along the ruler. If it doesn't end just past the 85 mark, reprint at 100%.
Or cut out the circles and slide them over your nipple. The smallest hole that fits around the base without pinching is your nipple size.
- 13 mm
- 14 mm
- 15 mm
- 16 mm
- 17 mm
- 18 mm
- 19 mm
- 20 mm
- 21 mm
- 22 mm
- 23 mm
- 24 mm
- 25 mm
- 26 mm
- 27 mm
- 28 mm
Starting flange size = nipple diameter + 2 to 4 mm. Size each side separately. From pumpstash.app/breast-pump-flange-size
Flange size chart
The starting size is the common flange size closest to your nipple plus 3 mm, the middle of the 2 to 4 mm range. Not every brand makes every size; inserts fill most gaps.
| Nipple | Range (+2 to 4 mm) | Start with |
|---|---|---|
| 13 mm | 15–17 mm | 16 mm |
| 14 mm | 16–18 mm | 17 mm |
| 15 mm | 17–19 mm | 18 mm |
| 16 mm | 18–20 mm | 19 mm |
| 17 mm | 19–21 mm | 20 mm |
| 18 mm | 20–22 mm | 21 mm |
| 19 mm | 21–23 mm | 21 mm |
| 20 mm | 22–24 mm | 24 mm |
| 21 mm | 23–25 mm | 24 mm |
| 22 mm | 24–26 mm | 24 mm |
| 23 mm | 25–27 mm | 27 mm |
| 24 mm | 26–28 mm | 27 mm |
| 25 mm | 27–29 mm | 28 mm |
| 26 mm | 28–30 mm | 28 mm |
| 27 mm | 29–31 mm | 30 mm |
| 28 mm | 30–32 mm | 30 mm |
Signs your flange is the wrong size
Check during a session at your usual suction. These signs come from the Cleveland Clinic and Medela's fitting guide.
Flange too small
- The nipple rubs the sides of the tunnel or can't move.
- Pain, cracks, or blisters on the nipple.
- A pale ring at the base of the nipple, or a purple nipple after pumping.
- Less milk than you'd expect.
Flange too big
- Areola gets pulled into the tunnel.
- Tugging or pain, or gaps where the flange meets your breast.
- A sore or discolored ring on the areola, or swelling after pumping.
- Low output even when you turn the suction up.
A good fit
- The nipple is centered and moves freely in the tunnel.
- Pumping doesn't hurt.
- Milk flows freely after letdown, and your breasts feel soft afterwards.
Should your flange be smaller than the chart says?
Maybe. The 2 to 4 mm rule is a convention, and a Cleveland Clinic breastfeeding medicine specialist notes there's no evidence-based formula behind it.
A 2024 pilot study in the Journal of Human Lactation had 36 exclusively pumping parents use two fits for a week each: the usual manufacturer sizing (21 or 24 mm) and a closer fit chosen from the nipple tip measurement (13 to 19 mm, most often 15 mm). With the closer fit, they rated comfort higher and pumped about 15 g more per session on average.
It's one small study, and one of its authors teaches the sizing method it tested. Still, if the chart size pulls areola into the tunnel or never feels right, a smaller flange or insert is worth a try. An IBCLC (International Board Certified Lactation Consultant) can size you in person.
See whether the new size pumps more
PumpStash logs every session with its volume, so you can compare a week on your old flanges with a week on the new ones instead of going by feel.
Download for AndroidRelated tools and guides
- Power pumping schedule and timer An hour of pump-and-rest intervals to bring a dipped supply back.
- Exclusive pumping schedule by age How many sessions a day, and how to drop one without losing supply.
- Printable pumping log Track each session on paper to compare flange sizes.