How to select a breast pump flange size is a question I had in mind when I was pregnant. I asked a lot of friends and googled it, but didn’t think I could find a solid answer AT ALL. Therefore, I’d like to share what I know to help those who have the same questions.

Most of all breast pumps come in with a set of standard 24mm flange, which is what would fit most women. However, one size doesn’t fit all, just like not all women wear the same bra size.

Medela’s website has a flange sizing chart that you can reference. This is all great, but when figuring out the real size that you need, their instruction is not that accurate (my experience). My recommendation is to follow the instruction but still keep in mind that you might need a size bigger or two. Here’s what happened to me: I measured to be size 21mm before labor, but post-labor the lactation consultant said I needed size 27mm!!!?!!! SO if I were to only bought a pair of 21mm then I’d have no flanges to use once I got home! Luckily that I purchased those sizing kits online, so when I got home I have a pair of 27mm to use right away (Here are two flange sizing kits ranges from 19-24mm or 24-27mm that fits Medela Breast Pumps (Pump in Style, Lactina, Symphony) by Maymom.)

It doesn’t mean that nipple size would grow post-labor. It’s just that most of the sizing chart doesn’t show a good description about how to measure. Your areola will be sucked into flange but not too much, and this is the part that you’ll feel if it fits when you actually start using a breast pump. If the flange is either too big or small, you’ll feel discomfort (sometimes pain) when pumping. Therefore, the right flange size is when you don’t feel anything at all when pumping. (this also means there should be a small distance between your nipple and the flange (breast shield) walls.

For Philips Avent breast pump, unfortunately, they only come in one size, 24mm. Medela has the most size variations, and Spectra USA has a few size options, too. So it is very important to measure it correctly, depending on which breast pump you plan to use/buy. See my article about comparing breast pumps.

If you’re really on a tight budget that doesn’t allow you to purchase those sizing kits, you can try to measure the base of your nipple size, not the width of your nipple. (See my poor drawing below. The graph on the left is correct, whereas on Medela’s sizing chart it’s showing the one on the right).

Let me know if you have any questions, and feel free to drop me a message. Happy pumping!