Our flanges don't correspond directly to millimeter sizes. Regular flange measurements are taken at the sharp and abrupt corner from the flange to the tunnel area, which is the frequent culprit of pumping pain. Our flanges have a gradual transition from the "funnel" to the "tunnel," so they can't be measured in the same way.
XS — 15-18mm
Small — 18-23mm
Medium — 24-27mm
Large — 27-30mm
XL — 30-40mm
In our flanges, we find that measurements can give a general idea but you really do have to try the flanges out to find which one is right for you since there are many factors that play into sizing beyond the nipple width measurement, such as elasticity and nipple structure.
We strongly recommend taking our Sizing Quiz to figure out what size you need in our flanges, which may be different from what you've used before. If the size you end up needing isn't in the set you get and you're in the U.S., just let us know and we'll send it to you at no cost through our Size Guarantee.
Reviewed by Jenn Foster, MA, IBCLC, CD
February 8, 2022