If pumping feels uncomfortable or you’re not getting much milk, it may not be your body.

It may be your flange size.

This is one of the most overlooked parts of pumping, yet it can make a huge difference in:

• Comfort
• Milk output
• Pumping efficiency
• Nipple health
• Your overall experience

Many moms assume pain or low output means they’re “doing it wrong.” Often, the issue is simply the wrong fit.

New to pumping? Start here first: Pumping Breast Milk: Schedule, Storage & Tips

What Is a Flange?

A flange (also called a breast shield) is the funnel-shaped part of a breast pump that fits over your nipple.

Its job is to:

• Create a seal
• Allow the nipple to move freely in the tunnel
• Stimulate milk flow
• Support effective milk removal

When it fits well, pumping should feel:

• Comfortable
• Efficient
• Sustainable
• Not painful

Why Flange Size Matters

Using the wrong flange size can lead to:

• Pain or pinching
• Nipple swelling or damage
• Reduced milk output
• Longer pumping sessions
• Friction or rubbing
• Blocked ducts
• Frustration and early pumping burnout

And many moms are using the wrong size without realizing it.

If pumping hurts, also read: Common Breastfeeding Problems (and How to Fix Them)
If output is a concern: How to Increase Milk Supply Naturally

How to Measure Your Flange Size

Step 1: Measure Your Nipple (Not the Areola)

Use:

• A ruler with millimeter markings
• A nipple sizing tool
• Printable sizing guide from pump brands

Measure the diameter of the nipple only, not the darker areola around it.

Best time to measure:

• After nursing
• After pumping
• When the nipple is naturally extended

Early postpartum? Size can change due to swelling or hormones.

Read: Postpartum Recovery Tips for New Moms

Step 2: Add 2–4 mm

Most moms need a little extra room for movement.

Example:

• Nipple measures 17 mm
• Try a 19 mm or 21 mm flange

This is a starting point, not a guarantee.

Step 3: Test and Adjust

Numbers help—but comfort and output matter most.

You may need to try:

• One size smaller
• One size larger
• Silicone inserts for a custom fit

Signs Your Flange Size Is Wrong

Too Small

• Nipple rubs painfully against tunnel sides
• Pinching sensation
• Slow milk flow
• Nipple looks compressed after pumping

Too Large

• Too much areola is pulled into the tunnel
• Swelling or puffiness
• Weaker suction feel
• Less efficient milk removal

Just Right

• Nipple moves freely
• Minimal areola drawn in
• Comfortable suction
• Better output
• No damage afterward

Not sure if feeding is going well overall? Read: Signs Baby Is Getting Enough Milk

General Flange Size Chart

Always prioritize comfort and results over charts alone.

Tips for a Better Pumping Fit

1. Recheck Fit Regularly

Your body changes—especially:

• In the first 12 weeks postpartum
• During weaning
• With hormonal shifts
• If swelling changes

2. Use Inserts if Needed

Many moms need a smaller tunnel than what standard pumps include.

Silicone inserts can improve fit dramatically.

Especially helpful if you’re using a 24 mm flange but need something smaller.

3. Don’t Assume the Included Size Fits

Many pumps come with:

• 24 mm
• 28 mm

But many moms actually need:

• 15 mm
• 17 mm
• 19 mm
• 21 mm

Read: Best Electric Breast Pumps for New Moms

4. Watch Comfort + Output Together

The right flange often improves:

• Milk output
• Session speed
• Comfort
• Consistency

Pain While Pumping? Check This First

If pumping hurts, many moms assume:

• Low supply
• Pump failure
• Sensitive nipples
• “I’m just bad at pumping”

But flange fit is one of the first things to troubleshoot.

A small size change can make a major difference.

Flange Size and Milk Supply

An incorrect flange may reduce milk removal.

And incomplete milk removal can signal your body to make less milk over time.

The right fit helps:

• Empty the breast more effectively
• Protect supply
• Shorten sessions
• Improve pumping confidence

Read: How to Increase Milk Supply Naturally

Cleaning and Replacement

To keep pumping comfortable:

• Clean after every use
• Replace cracked or worn flanges
• Check valves/membranes too
• Replace stretched inserts when needed

A Gentle Reassurance

If this feels confusing, you’re not alone.

Most moms are never taught flange sizing.

They figure it out through trial and error.

You’re not doing it wrong.

You’re learning something many parents only discover later.

Finding the right flange size can completely change your pumping experience:

• Less pain
• Better output
• More confidence

Sometimes the biggest improvement comes from a very small adjustment.

You May Also Find Helpful

• Pumping Breast Milk: Schedule, Storage & Tips
• Best Electric Breast Pumps for New Moms
• Manual Breast Pumps
• Best Breast Milk Storage Bags
• Combination Feeding: How to Breastfeed and Bottle Feed Successfully

FAQ

How do I know if my flange is too small?

Signs include pinching, rubbing, pain, slow milk flow, or the nipple rubbing the tunnel sides.

Can the wrong flange size reduce milk supply?

Yes. Poor milk removal over time can affect supply.

What flange size do most moms need?

Many pumps include 24 mm flanges, but many moms need smaller sizes like 17–21 mm.