How to Choose the Right Breast Flange Size
The wrong flange size is the #1 cause of pumping pain and low output. Here's how to measure, what to look for, and how to know when your fit is right.
If pumping hurts, or you're not getting much milk, the culprit is very often the same thing: flange size. The flange is the funnel-shaped part that fits over your breast, and getting the right size makes an enormous difference to both comfort and output. Most people start with the size that came in the box and never realize it isn't right for them.
What the flange does
During pumping, your nipple is drawn into the flange tunnel. The right size lets your nipple move freely in the tunnel without rubbing the sides, while keeping most of the areola outside. Too big or too small, and you lose comfort, output, or both.
How to measure your nipple
Flange sizing is based on your nipple diameter, not your breast size. To measure:
- Using a ruler or measuring tape (in millimetres), measure the diameter across your nipple — just the nipple, not including the areola.
- Measure after a pumping session when the nipple is everted, for the most accurate reading.
- Add about 1–2 mm to your measurement as a starting point for flange size.
Sizes aren't one-size-fits-all: Flanges come in a range of sizes (commonly from around 16mm up). Many people need a smaller size than the standard one included with most pumps.
Signs your flange is too big
- Too much of your areola gets pulled into the tunnel
- Rubbing or chafing around the areola
- Reduced output despite good suction
Signs your flange is too small
- Your nipple rubs painfully against the sides of the tunnel
- The tunnel feels tight or pinching
- Your nipple turns white or you feel discomfort
- Whitening or a ring forming at the base of the nipple
Signs of a good fit
- Your nipple moves freely in the tunnel without rubbing
- Little to no areola is pulled in
- Pumping is comfortable
- You're emptying well
Don't be afraid to try a few sizes
It's completely normal to need a different size than what came with your pump — and your two sides may even need slightly different sizes. Spectra offers a range of flanges and breast shields so you can find your fit. If you're struggling, a lactation consultant can help you size correctly.
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Learn about the LC Program →This article is for general educational purposes only and is not medical advice. Every breastfeeding journey is different. Please consult your doctor, midwife, or a licensed lactation consultant for guidance specific to you and your baby.