The right breast pump flange size

The flange (or breast shield) is the funnel-shaped part that goes on the breast. Many pumps come with 24 mm flanges, but not every mother is that size. A flange that doesn't fit can cause pain, sore nipples, blocked ducts and less milk.

Updated 7 October 2026

In short

Measure the diameter of your nipple in millimetres, without the areola.
Add about 1–3 mm and that's your starting point for the flange size.
While pumping, the nipple should move freely in the tunnel without pain.

How to measure

Get a ruler or a tape measure with millimetres. You can also use a ruler printed at 1:1 scale.
Measure your nipple shortly after a feed or pumping session, when it has its usual shape.
Measure the diameter of the nipple at the base, from one side to the other. Don't include the areola, the darker area around it.
Add about 1–3 mm. For example, if your nipple is 17 mm, try a flange of about 18–20 mm.

Breasts aren't identical. You may need a different size for each breast, and the size can change over the weeks and months. Measure again if pumping starts to hurt or your milk decreases.

How to tell while pumping

Measuring is only the start. The best way is to see and feel how the flange behaves while you pump.

↔ Scroll sideways to see it all

Flange	What you see and feel
Too large	Along with the nipple, a lot of areola is pulled into the tunnel. The areola rubs against the tunnel walls and can become red or sore.
Too small	The nipple rubs against the tunnel walls the whole time. It comes out red, white at the tip or sore, and milk flows with difficulty.
Just right	The nipple moves freely back and forth in the tunnel. Little or no areola is pulled in. It doesn't hurt and the breast feels softer after pumping.

If you need a different size

Many brands sell flanges in different sizes for their pump.
There are also silicone inserts that fit inside a 24 mm flange and make it smaller. They're an inexpensive way to try different sizes.
Keep suction at the highest level that is still comfortable. Stronger suction doesn't mean more milk.
If you're not sure, a lactation consultant can help you choose.

Track it with Ditari i Bebes

In Ditari i Bebes you log how much milk you express each time. If the amount changes after you switch flanges or parts, you'll see it straight away.

See the app

Sources

This guide is for information only and doesn't replace advice from your doctor, midwife or lactation consultant. Every mother and every baby is different. If something worries you, talk to your doctor.