Breast pump flange size calculator
Find your fit in seconds — Spectra, Medela, Momcozy, Elvie & Willow.
Enter your nipple diameter and get the right breast pump flange size for Spectra, Medela, Momcozy, Elvie, and Willow pumps. This breast pump flange fit guide includes a measuring guide so you can find your size at home — wrong flange fit is the most common cause of pumping pain and low output.
Why flange size matters
Wrong flange size is the single most common cause of pumping pain and low output. A flange that is too small pinches your nipple; one that is too large pulls in areola and reduces suction. Most pumps ship with 24 mm flanges, but many moms need 15–21 mm or 27 mm plus.
Getting the fit right can feel like unlocking a new pump — output often improves within days. Track sessions before and after a flange change to see whether fit was the bottleneck.
For a deeper dive, read our breast pumping flange size guide. If pumping hurts, see breast pumping nipple pain.
Frequently asked questions
How do I measure my nipple diameter at home?
Use a ruler or caliper in millimeters. Measure the width of your nipple at the base — not the areola — at rest or after one to two minutes of pumping when the nipple is slightly elongated. Add 2 mm to get your starting flange size.
What flange size is right for Spectra pumps?
Spectra flanges come in 16, 20, 24, 28, and 32 mm. Enter your nipple measurement above and select Spectra to see your recommended size. Most moms need smaller than the default 24 mm kit flange.
Can I use a different brand's flange with my pump?
Sometimes — if the flange connects securely to your pump and maintains suction. Many moms use third-party flanges or inserts. Check compatibility with your pump model before buying.
What happens if my flange is too small?
A too-small flange pinches the nipple against the tunnel walls, causing pain, blanching, and reduced output. You may see a white stripe on the nipple after pumping.
Does flange size change after birth or over time?
Yes. Nipple size can change in the first weeks postpartum and again after weaning or during pregnancy. Re-measure if pumping becomes painful or output drops unexpectedly.
Why does pumping still hurt if my flange size is correct?
Fit is only one factor. Check suction level, elastic nipple tissue, valve wear, and technique. See our guide on breast pumping pain and nipple soreness for troubleshooting steps.
