You're standing in front of the mirror, or scrolling through a shop with a nursing bra sitting in your basket, and then the question hits: what size do I actually order? Your old pre-pregnancy size tells you nothing any more. Your breasts feel heavier, fuller, different from a few months ago. And that's exactly the problem: you often simply don't know what your breasts are doing right now. So you hold off ordering, because what if it doesn't fit.
There's something else going on too. Search for a "nursing bra that really supports" and the instinct is quick to follow: I'll just take it a touch tighter or smaller, because tight holds everything in place. It works the other way round. A tighter bra doesn't give you more support. It gives you pressure points. And those red marks aren't proof that it's sitting snugly, they're a warning that it's too tight.
Short answer, in two parts. One: measure your size again, now, because your old size is no longer a reliable starting point. Two: a good nursing bra should feel like support, not like a squeeze. Support comes from a band that sits flat and evenly, not from pulling it tight. Below you'll read how to measure now, how to use two fingers to check the fit, and why those two things blur into each other more easily than you'd think.
Why your old size no longer fits
Your breasts change twice during this time, and both times by quite a lot. First in pregnancy: under the influence of hormones your breast tissue grows and your ribcage widens. Then again when your milk comes in, usually around day three to five after the birth. That's when your breasts fill up and can become noticeably larger and tighter within a day.
That's no small difference. In mothers' own stories you see huge variation: one goes from a DD cup to a G cup in the first months, another gains two cup sizes, and for someone else it barely shifts. That's the whole point. How much your breasts change can't be predicted from your old size. One woman goes up a single cup, another three, and for many it later settles partway back.
What that means for you: the size you wore before pregnancy is not a reliable starting point. You measure again, in the phase you're in right now. And you assume it will still shift. That's not annoying to know, it's actually reassuring, because it takes the pressure off guessing that one perfect size.
How to measure your nursing bra size now
All you need is a tape measure and two measurements: the band and the cup. Do it ideally late in pregnancy or in the first weeks after the birth, once your breasts have already changed, so you measure what you have now.
1. The band
Measure horizontally around your ribcage, just under your breasts. The tape should sit firmly but still move as you breathe, so don't hold your breath and don't let it cut in. Round the number in centimetres to the nearest standard band size (65, 70, 75, 80 and so on). This number carries the most weight: it's the band, not the straps, that supports your breasts.
2. The cup
Next, measure loosely around the fullest point of your breast, keeping the tape level across your back. The difference between this bust measurement and your band measurement sets your cup: the bigger the difference, the bigger the cup. Roughly, every 2 to 3 centimetres of difference stands for one cup size. If you measure around 12 centimetres more than your band, for example, you're around a D cup.
3. Expect it to keep shifting
Important: this is a snapshot, not a final size. In the first weeks your breasts swell by the day, sometimes by the feed. That's why many nursing bras don't use rigid, fixed number sizes but a bit of stretch, or sizes like S, M and L. That's not a cheap shortcut, it solves exactly your problem: you don't have to hit the exact size, because the bra moves with the milk that comes and goes through the day. If you want to know the best moment to buy your first nursing bra, read when to buy a nursing bra.
Why a tighter bra doesn't give more support
Here's the mistake almost every mother makes when she's after "real support". The logic feels right: tighter holds everything better, so tighter supports better. In practice it works the opposite way.
Support comes from a band that sits flat and evenly across your whole ribcage. A band like that spreads the weight of your breasts over a broad area and stays horizontal. Pull that same band tighter and you don't spread the weight better, you concentrate the pressure onto a few spots. You feel it in red marks on your skin when you take the bra off, in a band that cuts into your side, or in straps that dig grooves into your shoulders. Those aren't signs of good support. They're signals that the bra is too tight.
And with breastfeeding that's more than just discomfort. A bra that's too tight can put pressure on your milk ducts. That's why La Leche League advises against underwired bras and tight, pinching styles, especially in the first months, because sustained pressure on full breast tissue can contribute to a blocked duct. There's no hard, settled proof, but it's a sensible precaution: your breasts swell day and night, and you want nothing cutting into that full tissue. So too tight actually works against the breastfeeding itself.
If you have a larger cup and feel that ordinary stretchy bras don't support you enough, the answer isn't tighter but better fitting: a firm, wide band and wide straps that carry the weight. There's more on how to spot a pinching or badly fitting bra in the signs of a poor fit or compression.
The two-finger test: how to feel whether it fits
You don't have to guess whether "supportive" has tipped over into "pinching". There's a simple line you can feel with your hands.
- Under the band, at the back: you should be able to slide two fingers flat between the band and your back. If they don't fit, the band is too tight. If the band rides up towards your shoulder blades or you can pull it far away from your back, it's too loose and your breasts miss out on support.
- In the middle, at the front: the little piece of fabric between your cups should lie flat against your breastbone. If you can fit one finger comfortably behind it, that's right.
- The straps: you should be able to slide a finger under them without them cutting into your shoulder. If you're drawing the support from the straps instead of the band, you get the grooves in your shoulders, and that shouldn't happen.
- The cup: your breast should fill the cup completely, without tissue bulging over the top or sides, and without the cup wrinkling because it's too roomy.
If it sits like that, you have support without a squeeze. If it feels tight, if you see red marks, or if you notice a tender, hard spot where the bra presses, that's your cue to switch or adjust a size. The common miss is a too-tight band with a too-roomy cup, when it should be the other way round. Support comes from a well-fitting band, not from pulling the band extra tight.
So should I buy a size bigger?
Some mothers deliberately buy the band a bit roomy, out of fear of pinching. That's just as much a trap the other way. A too-loose band rides up and stops supporting. The better approach: choose the band so it sits flat and horizontal without pinching, and give the cup a bit of room for the swelling still to come. A bra with some stretch in the band and cup absorbs that fluctuation without you having to guess in either direction.
When pressure marks are a reason to get in touch
A bra that pinches, you take off and swap. Usually that's the whole story. But a few things don't belong under "just wore a tight bra for a bit" and deserve a proper look. Contact your GP or midwife, or in the daytime a lactation consultant, if you have:
- A fever or a fluey, run-down feeling together with a breast complaint.
- A red, warm, painful patch or a hard zone in your breast, especially if you feel yourself getting rapidly more unwell. This can point to mastitis - an inflamed breast that can develop into an infection.
- A hard spot or lump that doesn't clear after a feed or after a few days.
- Bloody or unusual nipple discharge that comes from only one breast, persists, or smells or looks odd, separate from cracked nipples.
For breastfeeding support you can turn to your health visitor or a local infant feeding team. But with a fever or a red, painful breast, your GP is the first port of call, not a support line; out of hours, contact your out-of-hours GP service or NHS 111. A well-fitting nursing bra keeps you comfortable and dry. It's not a fix for a medical complaint, and it should never hide one either.
A nursing bra that supports without pinching
We built our nursing bra around exactly this one point: support from a band that fits, not from pulling it tight. It's wireless, and the band gives as your breasts swell, so it moves with the fluctuation instead of cutting into it. The straps are wide, so the weight rests on your band and not in your shoulders.
The clip opens one-handed, handy for feeding, including at night in the dark. And because the leak protection is already built into the cup (four layers, with a core that catches up to 30 ml per cup), there's no loose breast pad that can slip away. Knitted from an OEKO-TEX Class I certified fabric (certificate number 11-36224), the strictest category, for textiles that touch the skin of babies under three. Designed in Belgium, knitted in Türkiye.
Want to take a look, you can do that here: see the nursing bra. And if you'd like everything about nursing bras, fit and wearing comfort in one place first, head to the guide to nursing bras, fit and comfort.
Frequently asked questions
I don't know what size I am now, so how do I order a nursing bra?
Measure again, in the phase you're in now, because your old size often no longer fits. Take two measurements: the band firm but breathing under your breasts, and loosely around the fullest point for your cup. Expect it to keep fluctuating, so choose a bra with some stretch, so you don't have to hit the exact size.
How do I know whether my nursing bra fits?
Use the two-finger test. At the back, two fingers should slide flat between the band and your back, and at the front one finger behind the centre piece. The band sits horizontal and doesn't ride up, the cup fills without tissue bulging over, and the straps don't cut into your shoulders. That's how it supports without pinching.
Are red marks or pressure marks after wearing it normal?
No, they aren't. Red marks and pressure marks mean the bra is too tight in that spot. They're not a sign of good support, but a signal to switch or adjust your size. Sustained pressure on full breast tissue can also contribute to a blocked duct, so don't put up with it, change it.
Should I buy a size bigger for breastfeeding?
Not automatically. A too-loose band rides up and gives no support, a too-tight one pinches. Choose the band so it sits flat and horizontal without pinching, and give the cup a bit of room for the swelling still to come. A bra with stretch in the band and cup absorbs the fluctuation without you having to guess.
My breasts keep changing, how many nursing bras do I need?
Count on change rather than on one size. Measure again when you notice your bra getting tight or turning roomy. A nursing bra with stretch bridges the small daily fluctuations, so you don't have to buy a new set at every phase. Keep enough on hand to rotate while one is in the wash.
Read on in this guide
- The signs of a poor fit or compression
- Which nursing bra is genuinely leak-proof? Absorbent options compared
- When to buy a nursing bra: pregnancy or the early days?
- Night-time leaking: what to wear in bed without soaking through
- Nursing bras, fit and wearing comfort: the overview
