Correct Flange Size When Pumping
Almost every pump ships with a 24mm flange. Almost nobody needs 24mm. That single mismatch is behind more pumping pain and more low-output panic than anything else I hear about.
The flange, or breastshield, is the funnel-shaped part that sits over your nipple. Get the size wrong and you get discomfort, inefficient milk removal, and sometimes real tissue damage. Get it right and pumping stops being something you brace for.
How to find your size, in three steps
- Measure your nipple diameter at the base, before pumping, not including the areola.
- Add 0 to 3mm. A 16mm nipple points to a 16–19mm flange.
- Start at the smallest size in that range and assess comfort, flow, and how empty you feel afterwards.
Why sizing matters
Proper sizing does two jobs at once: it makes pumping comfortable, and it makes milk removal efficient. You are aiming for no pain, strong sprays, and breasts that feel genuinely empty at the end.
How to measure
Measure before you pump, when your nipple is at its resting size. Our free Flange Fit Guide includes a printable measuring tool if you want something to hold against yourself rather than guessing.
Then add 0 to 3mm to that measurement and start at the smallest size in the range. Sizing down is far more commonly the fix than sizing up.
What a correct fit looks like
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Five signs your size is wrong
- Areola is pulled into the tunnel, or milk flows back towards you. This is the most common problem by far. Too much tissue drawn in compresses your ducts and ruins the seal, so milk runs back instead of into the bottle. The fix is almost always sizing down, not up.
- Your nipple rubs the sides of the tunnel. This one usually does mean the flange is too small. But if your nipple swells to rub the sides no matter what size you try, you may have elastic nipples, which is a different problem with a different fix — and sizing up will make it worse.
- Red or white rings and patches on your breast after a session. The flange is putting excessive pressure on the tissue.
- Any discomfort at all. Soreness, pinching or aching during or after pumping is not something to push through. It is information.
- Your breasts still feel full when you finish. Hand express to check. If milk is left behind, the fit is not letting you drain effectively.
Once the fit is right
Find your suction sweet spot: turn it up until it becomes uncomfortable, then dial back slightly. IBCLCs call this maximum comfort vacuum. Higher suction does not mean more milk. It means potential tissue damage and, because pain triggers adrenaline, often less milk.
From Idaho Jones
The comfortable flange, in your exact size
If sizing has meant pain, rubbing or red rings, Cushy is soft silicone instead of hard plastic, in 2mm steps from 13 to 30mm so you can dial in the fit. Designed with IBCLC Jessica Anderson for sensitive and elastic nipples.
Shop Cushy flanges →Not sure which size is yours? Try 3 sizes for the price of 2 and keep the one that fits →
A last word
Every body is different, so do not be discouraged if the first size is not the one. Sizing is a process of narrowing down, not a single correct answer you either find or miss. And if you have worked through this and pumping still hurts, a lactation consultant with flange sizing experience can assess you in person.
Still not sure what size you are? Write to [email protected] and tell me what is happening — it comes straight to me. Ece x
