If you've searched "44DD nursing bra" or "36DDD nursing bra" at 2am, half-asleep and not sure your usual size still applies - you're not overthinking it. That search is one of the most common ones we see, and there's a reason: almost nobody explains how nursing bra sizing actually works, so you're left guessing at exactly the moment you have the least energy to guess.
One quick note before we go further, since we ship to NZ, Australia, the UK and the US, and sizing labels aren't identical everywhere. None of that changes the myth below - it just means the same fit can carry a different label depending on where you're shopping from. Here's how cup and band sizes actually line up:
Cup Size Conversion
|
UK / NZ / AUS |
USA |
EU |
|
D |
D |
D |
|
DD |
DD / E |
E |
|
E |
DDD / F |
F |
|
F |
G |
G |
|
FF |
H |
H |
|
G |
I |
I |
|
GG |
J |
J |
|
H |
K |
K |
|
HH |
L |
L |
|
J |
M |
M |
Back (Band) Size Conversion
|
UK / USA |
NZ / AUS |
EU |
|
28 |
6 |
60 |
|
30 |
8 |
65 |
|
32 |
10 |
70 |
|
34 |
12 |
75 |
|
36 |
14 |
80 |
|
38 |
16 |
85 |
|
40 |
18 |
90 |
|
42 |
20 |
95 |
|
44 |
22 |
100 |
|
46 |
24 |
105 |
So a NZ/AUS size 12E is a UK 34E, which is a US 34DDD/F - same fit, three different labels. Worth bookmarking next time you're guessing at 2am.
The Myth: Your Regular Size Carries Over
The most common assumption is that your pre-pregnancy bra size is still your size, just needs a nursing bra version of it. Close behind it is the other one: "any bra with clips will do." Both feel reasonable. Neither is quite right, and getting it wrong isn't just a comfort issue.
What Actually Changes (And What Doesn't)
Here's the part that surprises most people: your band and your cup change on different timelines. Your rib cage actually widens during pregnancy to make room as your organs shift, so your band size has often already gone up a size or two by the time you're nursing - it's not the number that stayed still. What keeps moving after that, week to week and sometimes day to day, is your cup, as milk comes in and your supply settles.
Your band moved once, earlier than you think. Your cup keeps moving, and it's usually the bigger, faster change of the two - which is exactly why checking your size again now matters, even if you already resized once during pregnancy.
That's why the band number from your last maternity bra can still be right, while the cup size next to it needs to be one, two, sometimes three letters bigger than anything you've worn since.
First pregnancy and no maternity bra to compare against? You don't need to start from a size chart. Start from the best-fitting regular bra you own - the one with no digging, no spilling, band sitting level all the way round - and use that as your baseline. From there, expect the band to have moved with your rib cage and the cup to keep moving as milk comes in, and size up from that starting point rather than guessing at a number cold.
Why Underwire Can Actually Be a Problem
This is the part that matters beyond comfort. A rigid underwire sized for your old cup doesn't just feel tight when your cup has grown - it presses directly on tissue that's now full of milk. That pressure can restrict flow in exactly the spot it's pressing on, and that's how a blocked duct starts. Left unaddressed, a blocked duct can progress to mastitis.
None of that is about the bra you own being bad. It's about a rigid structure being asked to hold a shape that's already moved past it.
|
A 30-Second Check • Underwire that presses, digs, or leaves a mark when you take the bra off - your cup has likely grown past it • Spilling at the top or sides, even when the band feels fine - a cup sizing issue, not a band one • A tender, firm spot that doesn't ease after a feed - worth checking with your midwife or lactation consultant, and worth checking your bra first
|
Knowing Your Cup Size Is Only Half the Equation
Even once you know your correct size, your body keeps moving through it - fuller in the morning, different again after a feed, different again in a week. That's exactly why a rigid structure is the wrong tool for the job in these early months. What actually works is a bra built to move with a cup size that isn't finished changing yet, with support that doesn't rely on wire to hold its shape.
|
Built To Move With You • Wirefree, so there's no rigid edge pressing on tissue that's already full • Flexible fabric that adjusts through the day, not just the week • Full support without a fixed cup shape working against you
|
Wirefree isn't a forever rule, either - it's just the right call while things are still settling. Once your milk has settled into a rhythm and your cup has stopped moving week to week, that's when flexiwire styles are worth introducing: a flexible wire that shapes and supports without the rigidity that caused problems in these early weeks.
The Short Version
Your band already moved once, back during pregnancy. Your cup is what's still moving now, more than you'd expect. A rigid underwire sized for the old you can press on tissue that's now full of milk, which is how blocked ducts and mastitis start. Knowing your cup size is only half the equation - the other half is choosing something built to move with a body that isn't finished changing.
From the team at Hotmilk
