Nursing bras are one of the few garments where buying early and buying well can both be mistakes. Size changes substantially between late pregnancy, the first week after birth, and the settled weeks that follow — so a bra bought in month seven of pregnancy may fit for a fortnight and then not at all.
Here is a timeline-based approach that avoids buying the same thing three times.
The three sizing stages
Stage 1 — Late pregnancy (roughly 36 weeks onward)
Ribcage has usually expanded to close to its maximum. Bust has grown but has not yet reached its largest point. This is a reasonable moment to measure, because the ribcage measurement is the more stable of the two and it is unlikely to change much more.
Stage 2 — The first week or two after birth
This is the most variable period, and volume can change noticeably within a single day. Nothing structured or fitted will work well here. This is the stage for soft, stretchy sleep bras — not for anything you paid a lot for.
Stage 3 — From roughly week six onward
Things generally settle into a more predictable pattern. This is when it makes sense to measure properly and buy the bras you will actually wear for months.
The practical takeaway: buy two cheap soft bras before the birth, and buy your proper nursing bras at around six weeks postpartum. Reverse that order and you waste money.
How to measure
Use a soft fabric tape. Measure over a thin, unpadded bra or bare skin — never over clothing.
Band measurement: wrap the tape snugly around your ribcage directly under the bust. Keep it level all the way around and check the back in a mirror; it always rides up. Breathe out normally and read it then.
Cup measurement: measure loosely around the fullest part of your bust, standing upright. The tape should touch but not compress.
The cup size is derived from the difference between these two numbers. Different regions use different conversion systems — UK, US, EU and Australian cup lettering do not line up — so always use the chart for the brand you are actually buying from, not a general conversion table.
One important timing note: if you are breastfeeding, measure roughly 30 to 60 minutes after a feed. Measuring at your fullest gives you a number you will only match a fraction of the time.
What to look for in the bra itself
Wire-free for the early weeks. Underwire sits on tissue that is changing rapidly and can press in places that are uncomfortable. Many people find wire-free more comfortable throughout, but the first six weeks in particular are not the time to experiment.
A band with four or more hook rows. Your ribcage measurement will keep changing gradually for months. Extra rows mean the same bra adapts rather than being replaced. Buy so that it fits on the loosest hook when new — that leaves you room to tighten as the band stretches with wear.
Clips you can open with one hand, without looking. Test this in the shop or as soon as it arrives. You will be doing it in the dark, one-handed, while holding a baby. Drop-cup clips vary enormously in how easy they are to work; some need two hands and a good look, which makes them close to useless in practice.
A full-drop cup rather than a slot opening. A cup that folds fully down gives much better access than a bra with a small horizontal opening.
Wide, adjustable straps. Narrow straps carry more weight per centimetre and dig into shoulders. Adjustable matters because strap length needs change too.
Breathable fabric. Cotton-rich or moisture-wicking blends over pure synthetics. Skin under a bra is warm and often damp, and breathable fabric makes a real difference to comfort.
Flat, smooth seams. Anything that presses a ridge into the skin will become uncomfortable over an eight-hour stretch.
How many do you need?
A realistic set for someone breastfeeding:
- Two soft sleep bras. Worn overnight and around the house. Stretchy, no clips necessary, no structure. These get worn the most in the first month.
- Two or three day bras. With clips and proper support. Three lets you have one on, one in the wash and one dry.
- One bra that works under fitted clothing, if you need that for work or going out. Seamless, smooth cup.
Five to six total. Fewer than three means you are washing constantly; more than seven and you will likely find you rotate the same three anyway.
Fit problems and what they mean
Band rides up at the back: band is too loose. Go down a band size and up a cup size to keep the same cup volume.
Cup gapes at the top: cup too large, or the style does not match your shape. This is common with moulded cups and less common with stretch or soft cups.
Tissue spilling over the top or side: cup too small. This is the most common issue postpartum, and it is worth re-measuring rather than assuming your size has stayed the same.
Straps digging in: the band is not carrying enough of the weight. A correctly fitting band should carry most of the support, with straps doing relatively little.
Anything that causes pain, pinching or restricted areas: take it off and speak to a lactation consultant, midwife or your care provider. Persistent discomfort is worth getting looked at rather than working around.
This article offers general fitting and buying guidance. It is not medical or lactation advice. For questions about feeding, discomfort or your individual situation, please speak with a lactation consultant, midwife or doctor.