Nursing Bra Sizes: When to Buy, How to Measure and How Sizes Change
A nursing bra has to fit a body that keeps changing: late pregnancy, the days when milk comes in, and the months after. Here is when to measure, how much room to leave, and how letter sizes and band-and-cup sizes compare.
Measure and buy nursing bras from about 36 weeks of pregnancy, when most pregnancy breast growth has happened. Choose a size that fits on the loosest hook, because the ribcage narrows again after birth, with a little spare room in the cup (about a finger's width) for the fullness when milk comes in, usually 2-4 days after birth. Buy one or two, then add more once your size settles, often around 6 weeks postpartum.
- When to buy
- from ~36 weeks
- Hook to fit on
- loosest
- Milk comes in
- usually day 2-4
- Size settles
- often ~6 weeks after
On this page
Bra size changes in pregnancy and breastfeeding
Both band and cup change, but not at the same time. Knowing the order is what stops you buying bras that fit for only a few weeks.
| Stage | What changes | What to buy |
|---|---|---|
| First trimester | Breasts often grow and become tender early, sometimes by a cup within weeks | Soft, wire-free maternity bra, fitted on the tightest hook |
| Second trimester | Ribcage widens; the band can grow a size or more | Maternity bra with extra hook rows, or a band extender |
| From about 36 weeks | Most pregnancy growth is done; band at or near its widest | 1-2 nursing bras fitted on the loosest hook, with some cup room |
| Days 2-4 after birth | Milk comes in; breasts are fullest, often by a cup or more | Stretch-cup or sleep nursing bras; avoid anything tight |
| About 6 weeks after birth | Supply and size usually settle; band narrows | Remeasure and buy the rest of your nursing bras |
| Weaning and after | Breasts may return to, or end up smaller or softer than, the pre-pregnancy size | Remeasure a few months after weaning before buying regular bras |
These are typical patterns, not rules. Some people change by several cups and others hardly at all. Measuring at each stage is more reliable than predicting.
How to measure for a nursing bra
- Measure the underbust snugly, tape level, after breathing out. Round to the nearest even inch (or nearest 5 cm for EU sizes). This is the band.
- Measure the bust loosely at the fullest point, wearing an unpadded bra. After birth, measure after a feed or pumping session, when breasts are least full, and note the difference before a feed.
- Subtract the band from the bust. Each inch is one cup (1 in = A, 2 = B, 3 = C, 4 = D, 5 = DD). The bra size chart lists every combination and conversions to UK, EU and French sizes.
- Choose the cup for the fuller state. If your before-feed and after-feed measurements differ by an inch or more, use stretch cups or the larger cup with a removable pad.
Which hook to fit on, and why
Bra bands are adjusted with hook rows, usually three or four. Where a new bra fits tells you how it can adapt:
- Maternity bras early in pregnancy: fit on the tightest hook. The ribcage will widen, and you need the looser rows later.
- Nursing bras from 36 weeks: fit on the loosest hook. After birth the ribcage gradually returns toward its pre-pregnancy size, and the tighter rows keep the band supportive.
- Nursing bras bought after 6 weeks postpartum: fit on the loosest hook, as with any new bra, so you can tighten as the elastic relaxes.
A clip-on band extender typically adds about 1-3 in (2.5-7.5 cm) of band for a few weeks of late pregnancy. It is cheaper than buying a bra that will be too big after birth.
Letter sizes vs band-and-cup sizes
| Letter size | Bra sizes it usually covers | Bust (in / cm) |
|---|---|---|
| S | 32B-32D, 34A-34C | 34-37 / 86-94 |
| M | 34B-34D, 36A-36D | 36-40 / 91-102 |
| L | 36C-36DD, 38B-38D | 39-42 / 99-107 |
| XL | 38C-38DD, 40B-40DD | 41-45 / 104-114 |
Letter sizes suit the first weeks and nights because their stretchy cups follow size changes between feeds. For daytime support above a D cup, choose a band-and-cup nursing bra with molded or seamed cups and a three- or four-row hook band. Brands differ, so match the bust and underbust numbers to each chart.
Nursing bra styles and how they open
| Style | How it opens | Good for |
|---|---|---|
| Drop-cup clip | Clip at the top of the strap; the cup folds down | Everyday wear; one-handed opening |
| Crossover / pull-aside | No clips; the cup pulls to the side | Sleep, early weeks, quick feeds |
| Side-access or A-frame | Cup drops but a frame stays in place | More support when the cup is open |
| Pumping or hands-free | Slits or panels hold pump flanges | Expressing milk without holding the flanges |
| Nursing sports bra | Drop cups or a front zip on a firm sports band | Exercise; see the sports bra size guide |
Fit checks while breastfeeding
- No pressure lines on the breast from cup edges, wires or seams after a few hours of wear.
- Room for a breast pad without the cup edge cutting in. Pads take a few millimeters of depth.
- Clips you can open with one hand while holding a baby.
- Band level and snug enough to support the weight of fuller breasts, with straps that do not dig in.
Soft bralettes work for some people at night or once supply settles. For other changes in pregnancy, see the maternity clothing size guide.
Frequently asked questions
How much bigger should a nursing bra be than my normal bra?
There is no fixed rule. Many people go up one or two cup sizes and one band size during pregnancy, but it varies widely. Measure at about 36 weeks rather than adding sizes to your old bra, and choose stretch cups or one cup size of room for when milk comes in.
Should a nursing bra be bought before or after birth?
Both. One or two from about 36 weeks cover the hospital stay and the first weeks. Buy the rest once your size settles, often around 6 weeks after birth, because breasts are at their fullest and most variable in the first days of breastfeeding.
Can I wear an underwire nursing bra?
Many breastfeeding advisers suggest wire-free or flexible-wire nursing bras, at least in the early weeks, because firm pressure on breast tissue is a commonly cited factor in blocked ducts. If you wear wires, make sure they sit on the ribcage around the breast, never on breast tissue.
What size nursing bra if I'm between sizes?
Choose the larger cup and the band that fits on its loosest hook. Cups that are slightly roomy can take a breast pad; cups that are tight press on the breast as it fills between feeds.
Do nursing bras come in S, M, L sizes?
Many do. Letter-sized nursing bras have stretch cups that cover several bra sizes, for example M for about 34B-36D. They tolerate size swings well but give less support to D cups and above than band-and-cup sizes.