This "breast pump flanging size tool" is small but VERY easy and straightforward to use.

It's pink, and well made & sturdy. Comes with a tin case, handy to store it and other things. Also comes with a QR code for a video showing you how to use it, and instruction page.

Basically, you line up your entire nipple into the ruler, with it resting at the base of your nipple. So it's snug but not so snug that your nipple can't move freely. And not so freely that it's not touching your nipple. Then you look to see what number that corresponds to, and that is your exact flange size. No guessing, no adding. I like that it fits your entire nipple and not just the base.

She also offers instruction on how to measure inverter and flat nipples through the video. All examples are shown with actual real nipples and not just on crocheted or plastic breasts.

Because of the different shape of my nipples, I was never sure of my right size. This has given me more confidence in knowing it's correct.

I would definitely recommend this product. Much easier to use than the paper printouts or plastic hole things you get with some pumps.

It's by Save the Milk. I was able to purchase it on Amazon with next day service, though you can get it through her website too.