How to Measure Your Nursing Bra Size During Pregnancy
Nobody warned me that buying a nursing bra would feel like solving a puzzle, in the dark, while sleep-deprived. I picked up my first one sometime around 20 weeks, grabbed what looked like my “usual” size, and thought I was sorted. Spoiler: I was not. By the time my milk came in, that bra was practically unwearable, and I was back to square one with a newborn in tow.
If you’re trying to figure out your nursing bra size during pregnancy, the good news is it’s genuinely not that complicated once someone explains it properly. The bad news? Most sizing guides skip the nuances that actually matter. So let me walk you through it the way I wish someone had walked me through it.
Why Your Regular Bra Size Doesn’t Work Anymore
Here’s something that caught me completely off guard: your pre-pregnancy bra size is basically irrelevant from about the end of your first trimester onward. Breasts typically grow one to two cup sizes during pregnancy alone, and then when your milk arrives in the first few days postpartum, they can increase by another cup size (sometimes more). Lactation consultants often describe this as one of the most underestimated physical changes new moms experience.
I noticed my band felt tighter even before the cup size change was obvious. That’s because breast tissue and surrounding chest muscles are both responding to hormonal shifts, not just the visible fullness. A lot of moms I’ve spoken to say they bought their nursing bras too early in pregnancy, ended up with a band that fit but cups that didn’t, or the other way around. Timing your measurement correctly makes a real difference.
When Is the Best Time to Measure for a Nursing Bra Size?
The sweet spot, and this one’s backed by most maternity fit experts, is around 36 to 38 weeks of pregnancy. By this point, your ribcage has expanded to near its maximum, and your breast size is close to what it’ll be during early breastfeeding (accounting for milk coming in). Measuring at 12 or even 20 weeks often leads to buying a bra that fits now but won’t work when you actually need it most.
That said, I’d still recommend buying a couple of bras with some size flexibility, especially in the cup. Your nursing bra size can shift again in those first two weeks postpartum when your body is regulating milk supply. Adjustable bands and stretchy cup panels aren’t just comfort features; they’re practical ones.
How to Actually Measure Your Nursing Bra Size at Home
You don’t need a professional fitter for this, though if you have access to one, absolutely use them. Here’s how to do it yourself:
Step 1: Measure your band size. Wrap a soft measuring tape snugly around your ribcage, just beneath your bust. Keep it level and breathe normally (don’t suck in). If you get an odd number, round up to the nearest even number. That’s your band size.
Step 2: Measure your cup size. Measure around the fullest part of your bust, usually across the nipples, while wearing a non-padded bra or nothing at all. Keep the tape parallel to the ground.
Step 3: Calculate the difference. Subtract your band measurement from your cup measurement. Each inch of difference corresponds to a cup size: 1 inch = A, 2 inches = B, 3 inches = C, 4 inches = D, and so on.
Step 4: Add a cup size. Here’s the part most guides miss: because milk coming in will increase your cup size, many lactation experts recommend sizing up one full cup when buying a maternity bra during pregnancy. So if you measure as a 36C, consider buying a 36D nursing bra to accommodate those early postpartum days.
Lovemère has a detailed Bra Fitting Guide that walks through this step-by-step with visuals, and it’s genuinely one of the clearer guides I’ve come across for doing this at home.
What to Look for Beyond Just the Size
Getting the numbers right is only half the job. The fit actually matters just as much, maybe more. A bra that’s technically the right size but has rigid underwire can press against developing milk ducts and contribute to blocked ducts or mastitis. That’s not a minor inconvenience; it’s a real medical concern that midwives and lactation consultants flag regularly.
For this reason, most experts (and honestly, most experienced moms) recommend soft-cup or wire-free nursing bras, especially for the first few months. Breathable fabric matters too. Your body runs warmer during breastfeeding, and a bra that traps heat can cause skin irritation faster than you’d expect.
When I was testing different styles, I found that bras with a drop-cup or crossover design were far more practical for feeding than I’d anticipated. You’re not thinking about aesthetics at 3am; you’re thinking about one-handed access. Lovemère’s nursing bra collection includes a range of wire-free styles designed specifically for this, and it’s worth browsing if you want options that balance comfort with practicality.
The One Thing Most Articles Don’t Tell You
Here’s something I genuinely haven’t seen covered often enough: your nursing bra size can shift multiple times, and that’s completely normal. It’s not a fitting failure. In the first week postpartum, breasts often feel engorged and larger. By weeks four to six, as your body settles into a feeding rhythm, that size may come down again. By the time you wean, you might be back close to your pre-pregnancy size, or not.
Buying two or three nursing bras in the same size and expecting them to last the entire breastfeeding journey isn’t always realistic. Many moms end up needing a slightly different fit at the three-month mark versus the newborn stage. If budget is a concern, investing in one or two quality bras with good adjustability is smarter than buying five cheaper ones in a single size.
Bringing It All Together
Measuring for a nursing bra isn’t hard, but it does require doing it at the right time, with the right approach, and with a little forward-thinking about what your body is about to do. Measure at 36 to 38 weeks. Get your band snug, your cup generous. Go wire-free. And don’t assume the size you buy at 30 weeks will still work at six weeks postpartum.
If you want to dive deeper into the whole nursing bra buying process, including how many you actually need, which styles work for different body types, and what fabrics hold up best through washing, check out our pillar guide: 5 Things I Wish I Knew Before Buying My First Nursing Bra. It covers a lot of the “why didn’t anyone tell me this” territory that goes hand-in-hand with sizing.
FAQ
Can I measure my nursing bra size in the first trimester?
You can, but it won’t give you an accurate picture of what you’ll need for breastfeeding. Most experts recommend waiting until around 36 to 38 weeks, when your body is much closer to its postpartum size. Early measurements tend to underestimate how much your breasts will change.
How many cup sizes do you typically go up during pregnancy?
Most women go up one to two cup sizes during pregnancy, with a possible additional increase when milk comes in postpartum. Individual variation is significant; some women experience more change, some less. Hormones, genetics, and whether you’ve breastfed before all play a role.
Should a nursing bra be tight or loose?
The band should be snug, supportive without digging in, and you should be able to fit two fingers underneath it. The cups should contain your breast fully without spillage or gaps. If you’re in doubt between sizes, size up in the cup (not the band) to allow for milk volume changes.
Is a maternity bra the same as a nursing bra?
Not exactly. A maternity bra is designed to accommodate breast changes during pregnancy but doesn’t necessarily have nursing access. A nursing bra has drop cups or panels that open for feeding. Many women use both, or choose a bra designed to work for both pregnancy and breastfeeding.
When should I start wearing a nursing bra?
You can start wearing one as early as late second trimester if you want the comfort of a softer, more supportive style. But the practical need, the drop-cup access for feeding, only becomes relevant once your baby arrives. Many moms start wearing nursing bras at around 36 weeks as a way to get used to the fit.
