Which breast pump is right for me, and how do I know the flange fits?

You bought a pump, opened the box, and there was a flange inside, so you assumed the size must be right. Why else would that particular one come in the box? You put it on and it hurts. It pinches, your nipple rubs against the wall, and after fifteen minutes there's barely any milk in the bottle while your breast still feels full. Then comes the thought so many mothers land on: pumping just hurts, apparently, or I'm not making enough milk.

Almost always, neither is true. The problem usually isn't your breast and it isn't your technique. It's the size of that flange. And here's what nobody tells you: the flange in the box is a guess, not a measurement. It's a standard size the manufacturer throws in because something has to be in there, not because it was matched to your nipple.

This article turns the blame around. You'll read why you almost certainly need a smaller flange than you think (not bigger), how to measure your own size in thirty seconds, the four signs that tell you a flange doesn't fit, and which type of pump suits which situation. Because the most expensive double pump performs badly with the wrong flange. Fit comes before pump.

Short answer: measure your nipple diameter first (in millimetres, at the base of your nipple and before you pump), then add roughly 1 to 3 mm. That's your starting size. The standard flange that came with your pump is usually 24 to 28 mm, while many nipples come out smaller, so you often need a smaller flange than you'd expect. If you notice pain, a nipple that rubs, too much areola being drawn into the tunnel, or little output while your breast still feels full, the size isn't right. Choose the type of pump to suit your situation (now and then, daily, on the go, or building up your supply), but sort out the fit first, because that decides whether pumping is comfortable and whether your breast drains properly. If it keeps hurting or your nipples come back damaged, speak to a lactation consultant.

The flange in the box is a guess, and usually too big

Here's the realisation everything hangs on. A flange (also called a breast shield) is the funnel that goes over your nipple. As you pump, your nipple is drawn up into the little tunnel. For a good fit, only your nipple should move in that tunnel, smoothly, without rubbing, with at most a small rim of areola coming along. If a big mouthful of areola gets pulled in too, the tunnel is too wide.

And that's exactly what goes wrong. The flange in the box is nearly always 24 to 28 mm. But many nipples come out smaller, often somewhere around 15 to 18 mm. Add the small margin and your starting size, for a lot of mothers, sits below the flange that came as standard in the box. So you often need a smaller flange, not a bigger one.

Why does almost nobody know this? Because it's counter-intuitive. Pain feels like pinching, and pinching feels like too small, so mothers reach for a size up. That makes it worse: in a wider flange, even more areola gets sucked into the tunnel, and that rubs and drags. Plenty of mothers describe exactly that doubt: their nipple measures around 10 mm, while the smallest flange they can find is 21 mm, and they wonder whether their nipple is somehow too small and whether that's why their areola gets pulled in. That gut feeling is usually right. The flange was too big, not them too small.

The turnaround comes down to the same thing every time: mothers with small nipples order a smaller flange separately, and then it works fine. That's the whole story. You aren't doing anything wrong. The size just wasn't right.

How to measure your nipple diameter (and why you measure again)

Measuring isn't precision work, but a few things make the difference between a guess and a real size.

• Measure the diameter of your nipple, not your areola. It's the width of the nipple itself (the part that sticks out), straight across the middle, at the base where it meets your breast. A ruler in millimetres, a printable measuring card, or the little gauge that comes with many fit kits all work.
• Measure before you pump, not after. Your nipple swells while you pump. Measure afterwards and you'll read too big and choose too wide a flange. Measure when your nipple is at rest.
• Add a small margin. Your nipple needs a little room to move freely without rubbing. About 1 to 3 mm on top of your measured diameter is a good starting point. That's a starting size, not a verdict: how it really sits, you only find out once you pump.
• Measure each breast separately. Left and right can easily differ by half a size or a full size. It's completely normal to use a different flange on each side.

And then the part most people skip: your size changes. Your nipples in the first week look different from how they look after a few months of feeding. Mothers often notice only in hindsight: their size shifted between the newborn weeks and, say, eight months on, and a kit with a gauge and several sizes was what made that difference visible. So measure again if pumping suddenly feels less comfortable or your output drops. The size that was perfect in month one can sit slightly too roomy or too tight by month four.

If you're stuck between two sizes, a fit kit with several sizes (or separate reducer inserts) is the easiest way to compare without guessing. You can work out which size fits instead of gambling on it.

The four signs your flange doesn't fit

You don't have to trust a number if you know what to watch for. Here are the four signs. One on its own can be enough, but together they almost always point to the size, not to you.

1. Your nipple rubs or pinches against the tunnel wall. It should move freely. If it drags along the side, the flange is often too small, or your nipple isn't centred. Rubbing is the one sign that points to a size too small, whereas too much areola drawn in (the next sign) points to one too wide. This is the pain mothers write about most. Many know that raw feeling from outside pumping too: turning over in bed at night, the nipple catches on the bra or the pad again, and you could just cry.
2. Too much areola gets drawn into the tunnel. As you pump, watch whether only your nipple moves or a broad rim of areola comes along too. A big mouthful of areola means the flange is too wide.
3. Pain that lingers, even after the session. Pumping can feel firm, but it shouldn't hurt and it certainly shouldn't leave you sore afterwards. If your nipple keeps throbbing, blanches white, or feels tender once you're done, that's a signal. Damaged, cracked or bleeding nipples don't belong to normal pumping.
4. Little output while your breast still feels full. The wrong flange can't draw your milk out properly. If you feel drained but there's little in the bottle, that's often because the flange is squeezing the milk ducts shut rather than helping them along. Comfort and output are the same problem here, not two separate things.

Why the wrong size also gives you less milk

This is the part that surprises mothers most: fit is about comfort and about how much milk you pump. If the tunnel is too wide and you pull areola in, the tissue around your milk ducts gets squeezed rather than moving freely. Your breast then drains less well. Exactly what you don't want, because a breast that doesn't drain properly eventually sends the signal to make less.

Turn it around and put on the right, often smaller flange, and many mothers notice two things at once: it stops hurting and more milk comes. Mothers say plainly that separate reducer inserts work so much better than the flange that came as standard with their pump, and that their output went up a lot. That's not luck and it's not a better day. That's the size.

So if you've spent weeks thinking you're not making enough milk, it's worth checking your flange size first, before you doubt your supply. Very often the answer is in the funnel, not in your body. If you still worry about whether you're making enough, a lactation consultant will talk through your rhythm and how you're building up, calmly and without rushing.

Which type of pump suits which situation

Now the size is clear, the second question: which pump? There are broadly four kinds, and which suits you depends on how often and what for you pump. But keep the thread in mind: no type can make up for the wrong flange size. Fit first, type after.

• Single pump (manual or electric). Pumps one breast at a time. Fine if you pump now and then: a single bottle for a rare evening out, or easing off a full breast. Cheaper and simple, but slow if you need it often.
• Double pump (electric). Pumps both breasts at once. This is the workhorse choice if you pump daily, for example because you're going back to work. Double pumping doesn't just save time, it also gives many mothers a better output because both breasts are stimulated together. If you're heading back to work, read how to fit it in and what your rights are in pumping at work: rights, rhythm and what to pack.
• Wearable or hands-free pump. Sits inside your bra, quiet and cordless, so you can carry on walking around or working while it runs. Very handy on the go or between tasks. Pay extra attention to fit here, because these models often need separate reducer inserts to centre your nipple properly. Mothers explain why those inserts make the difference: they keep the nipple lined up neatly in the wearable pump and make pumping more comfortable. Wearable is comfort and freedom, but only if the size is right.
• Hospital-grade pump (multi-user). The heaviest category, usually a rental. Meant for building up or boosting your supply, for example with a premature baby, a baby who isn't feeding well yet, or low output. Stronger and more efficient, but overkill if you just want to express the odd bottle.

If you're not sure which suits you, that's a good question for your lactation consultant, health visitor or infant feeding team. And if you mainly want to ease a full breast without building up a stash, a pump isn't always needed: sometimes hand expression or a passive collector is enough, which we explain in hand expression and antenatal expressing and milk collection shells, the Haakaa and the Ladybug: who are they useful for?.

When it's better to check in

The wrong flange size is usually a matter of adjusting, not a medical problem. Even so, there are moments when you don't rely on general tips but get in touch with a health professional.

• Bleeding, cracked or painfully damaged nipples from pumping. That's often a sign the flange doesn't fit, but damaged nipples deserve to be taken seriously. A lactation consultant will look at your size and your technique. If nipple pain carries on, also work through pain-free feeding and what to check first.
• Pain that stays, even with an adjusted size. If you've tried several sizes and it still hurts, something else is going on that's worth a proper look.
• Your output drops noticeably or you worry your baby isn't getting enough. A lactation consultant (IBCLC) can go through your rhythm calmly.
• A fever with a red, warm, painful patch in your breast and a fluey, run-down feeling. That fits a breast infection, which can come on faster when your breasts don't drain properly from bad pumping. Call your GP the same day; out of hours, contact your out-of-hours GP service or NHS 111.
• A hard, painful spot that doesn't clear after pumping or feeding. Carry on with your normal feeding or pumping on that side, but don't pump that breast extra empty or massage it firmly to work the spot out: that can make it worse. Get in touch if it doesn't improve or gets worse.

In the UK you can turn to a lactation consultant, your health visitor or a local infant feeding team for breastfeeding support. But with a fever or a red, painful breast, your GP or midwife is the first port of call, not a support line; out of hours, contact NHS 111. No question is too small for that.

The hours in between pumping

There's one thing nearly every pumping guide skips: what happens to your breasts between sessions? Precisely on the days you put a session off because it's busy, your breasts get overfull and you leak. Sitting there soaked at work or out and about is exactly what you don't want when you've already got enough on your plate.

We made our nursing bra for those hours. It's wireless and knitted from a soft, giving fabric, with a clip that opens one-handed so you can latch on quickly when you go to pump. The absorbent layer catches up to 30 ml per cup, so your top stays dry if you leak between two sessions or pump a moment later than planned. The fabric is OEKO-TEX Class I certified (certificate number 11-36224), the strictest category for textiles that touch a baby's skin. It won't choose your pump for you and it won't measure your flange. But it means you don't have to spend a day with a wet patch, and on a day like that, that's worth more than you'd think. If you want everything about pumping, storing and work in one place, head to the overview of pumping, storing and work. And you can take a look at the bra itself here: see the nursing bra.

Frequently asked questions about pump choice and flange fit

What flange size do I need?

Measure the diameter of your nipple (not your areola) in millimetres, at the base and before you pump. Add roughly 1 to 3 mm, and that's your starting size. The flange that came with your pump is usually 24 to 28 mm, while many nipples come out smaller, so you often need a smaller one. How it really sits, you only find out while pumping.

Why does pumping hurt?

Usually pumping pain isn't because pumping simply hurts, but because of the wrong flange size. If your nipple rubs against the wall or a lot of areola gets drawn in, it pinches and drags. Counter-intuitively, a smaller flange often works better than a bigger one. If the pain stays after you've adjusted the size, speak to a lactation consultant.

Why do I pump so little milk while my breast feels full?

A poorly fitting flange can't draw your milk out properly, because the tissue around your milk ducts gets squeezed rather than moving freely. Your breast then drains less well. So check your flange size first, before you doubt your supply: very often the answer is in the funnel, not in your body.

Single, double or wearable pump: which do I choose?

Choose to suit your situation. A single pump is enough if you pump now and then. A double pump is the workhorse choice if you pump daily or go back to work, because it saves time and often gives more output. A wearable pump is hands-free and discreet for on the go, but then pay extra attention to reducer inserts for a good fit. Fit always comes before the type.

Does my flange size change over time?

Yes. Your nipples in the first week look different from how they look after months of feeding, so your size can shift with them. Measure again if pumping suddenly feels less comfortable or your output drops for no clear reason. Many mothers use a different size later on than at the start, and sometimes a different one on the left and the right.

Read on in this guide

• Pumping at work: rights, rhythm and what to pack
• Hand expression and antenatal expressing: how and when
• Storing, thawing and safely carrying breast milk
• Managing heavy leaking: catch, absorb or ease off
• Everything about pumping, storing and work (the overview)