Nursing bra size guide: when to buy and how to fit it
Your breasts change size more in the first weeks of feeding than at any time in pregnancy. A good nursing bra keeps up.
Updated October 13, 2026 · sources checked October 13, 2026
In short
Buy your first nursing bras late in pregnancy, when your size has mostly settled, and choose stretchy, adjustable styles: breasts keep growing as milk comes in. Measure your underband and fullest bust, fit on the loosest hook, and check that nothing digs in. The NHS advises a comfortable, supportive bra and avoiding tight bras when breasts are sore. Have two or three.
Why sizing is tricky
Breasts grow in pregnancy and keep growing after the birth. In a small but detailed study, breast volume had increased by an average of about 145 ml per breast by the end of pregnancy, and by about 211 ml one month into breastfeeding compared with before conception, with wide variation between women (Cox et al., Exp Physiol 1999). The NHS notes that breasts often feel fuller around 2 to 4 days after birth, when the milk comes in.
So the rule is simple: buy for flexibility, not for a perfect fit on one day.
When to buy
| Moment | What to buy | Why |
|---|---|---|
| Second trimester | A comfortable, stretchy maternity bra if your usual bras feel tight | Growth during pregnancy |
| Around 36 weeks | 2 nursing bras with room in the cup and extra hooks at the back | Size has mostly settled; time to pack your hospital bag |
| First week after birth | A soft sleep bra and breast pads | Milk comes in, leaks are common |
| About 6 weeks after birth | Re-measure and buy more if needed | Feeding and supply usually settle into a pattern over the first weeks |
How to measure
- Wear a light, non-padded bra or none, and stand straight.
- Band: measure snugly around your ribcage, just under the breasts, with the tape level.
- Bust: measure loosely around the fullest part of the breasts.
- Use the brand's size chart: it is the only reliable conversion, as sizing differs between makers.
- Choose a size that fits on the loosest hook, so you can tighten as your ribcage settles after birth.
Fit checks in the mirror
- The band sits level all the way around and does not ride up at the back.
- The cup holds the whole breast with no tissue spilling over or pressing at the edges, including at the side near the armpit.
- The centre front rests close to your chest.
- Straps stay up without digging in.
- You can open the clip with one hand, the other holding a baby.
- Nothing presses hard anywhere: the NHS advice for sore breasts is a comfortable, supportive bra and no tight bras.
Styles and features
| Feature | Options | Points to weigh |
|---|---|---|
| Opening | Drop-down clip at the strap, pull-aside, crossover | Drop-down clips give the cleanest access; crossover styles suit sleeping |
| Structure | Soft stretch, moulded cup, underwired | Soft stretch adapts most easily to changing size; wired styles need a precise fit |
| Fabric | Cotton-rich, modal, microfibre blends | Breathable fabric is more comfortable with leaks and night sweats |
| Back closure | 3 to 6 rows of hooks | More rows mean more room to adjust |
| Pads | Removable inserts or separate breast pads | Change pads often to keep skin dry |
What you really need vs nice-to-have
| Really need | Nice-to-have |
|---|---|
| 2 day bras with one-hand clips and spare hooks | A third bra for the laundry gap |
| 1 soft sleep bra | A pumping bra, if you will express often or at work |
| Breast pads | Washable pads for later months |
| A comfortable, non-tight fit | Different styles for different outfits |
If you go back to work and express, or move to formula, a soft, supportive bra still matters while your breasts adjust.
Is this normal? When to call
Normal: breasts that feel much fuller around days 2 to 4, and a size that shifts over the first weeks. Call your GP, midwife or OB-GYN: a swollen, hot, painful area, a hard lump, or flu-like aches and a temperature. Loosen your bra and keep feeding or expressing meanwhile, as the NHS advises for mastitis. Emergency: call 911 (US) or 999 (UK). In the UK, NHS 111 if you are unsure where to go.
Care
Wash in a laundry bag on a gentle cycle and dry flat, as most labels advise, so the elastic lasts through months of daily wear. Have enough bras to rotate.
For latch and feeding rhythm, see breastfeeding basics. A nursing pillow completes the feeding setup.
Questions parents ask
When should I buy a nursing bra?
Late in pregnancy, often around 36 weeks, is a common moment: your size has mostly settled but there is still time to have one in your hospital bag. Buy with room to grow, since breast volume keeps increasing after the birth.
Can I wear an underwired bra while breastfeeding?
There is no strong research either way. What the NHS stresses is comfort and avoiding tight bras, especially if a breast is sore or swollen. Many women choose soft, wire-free bras for the first weeks and decide later.
How many nursing bras do I need?
Two or three for the day, so one can be washed while another is worn, plus one soft sleep bra to hold breast pads at night.
Sources
- NHS, Mastitis (wear a comfortable, supportive bra; avoid tight bras) checked October 13, 2026
- NHS, Breastfeeding, the first few days (milk coming in, breast pads) checked October 13, 2026
- Cox DB et al., Breast growth and the urinary excretion of lactose during human pregnancy and early lactation, Exp Physiol 1999 (PMID 10226182) checked October 13, 2026
Mamavela explains; it does not replace your midwife, doctor or pediatrician, who know your situation. If something worries you, call them. In an emergency, call 911 (US), 999 (UK) or 112.