A maternity bra should feel like a quiet kind of support: present when you need it, never digging in or asking more of your body than it can give. If you are searching for how to measure maternity bra size, the goal is not to chase one perfect number for every stage. It is to find a comfortable starting point, then leave room for the very normal changes of pregnancy, milk production, and postpartum recovery.
Your breasts may grow early in pregnancy, change again as your due date approaches, and shift once your milk comes in. Measuring at home takes only a few minutes, and it can help you choose bras, tanks, and sleepwear that support you through it all with a little more ease.
How to Measure Maternity Bra Size at Home
For the most useful result, measure while wearing a lightly lined, non-padded bra or no bra at all. A soft measuring tape is best. If you do not have one, wrap a ribbon or string around your body, mark where it meets, then measure that length with a ruler.
Take your measurements while standing naturally. Do not pull the tape so tight that it presses into your skin, and do not leave it loose enough to slip. Your body deserves a fit that feels supportive, not restrictive.
Step 1: Measure your band
Place the measuring tape directly under your bust, where the band of your bra sits. Keep the tape level across your back and breathe normally. Record the measurement in inches.
If you land on an odd number, most bra-sizing systems will have you round up to the next even number. For example, a 33-inch underbust measurement often begins with a 34 band. However, brands can fit differently, and maternity bras are often designed with more stretch than an everyday underwire bra. Think of this as a helpful starting point rather than a rule you must follow.
The band does most of the work when it comes to support. It should feel secure on the loosest hook when the bra is new, so you can tighten it as the fabric naturally relaxes over time. If it rides up your back, shifts during the day, or leaves deep marks, try a different band size or a more flexible style.
Step 2: Measure around the fullest part of your bust
Next, bring the tape around the fullest part of your bust. Keep it level and comfortably relaxed. You are looking for the circumference of your breasts, not a compressed measurement.
Write this number down, then subtract your band measurement from your bust measurement. The difference helps estimate your cup size. Many US size charts use the following progression: a 1-inch difference is generally an A cup, 2 inches is a B, 3 inches is a C, 4 inches is a D, and 5 inches is a DD or E. Each additional inch typically moves you up another cup.
For example, if your band measurement is 34 inches and your bust measures 38 inches, a 34D is a reasonable size to try first. But the way the bra feels on your body matters more than the label. Cup sizing can vary between brands, and soft nursing bras may fit several cup sizes comfortably.
Step 3: Check the fit, not just the number
Once you have a size to try, use a simple fit check. The center front of a structured bra should sit comfortably against your chest, while a wire-free bra should lie flat and feel smooth. Your breasts should fill the cups without spilling over the top, sides, or bottom.
The cups should not wrinkle or gap, either. Gaping can mean the cup is too large, but it can also happen when the bra style is not shaped for your breast shape. Adjust the straps before deciding. They should stay in place without carrying all the weight of your bust or leaving grooves in your shoulders.
With a nursing bra, open and close the nursing clips once or twice. You want easy one-handed access, especially for those middle-of-the-night feeds when everyone is tired. A good nursing bra should make feeding simpler while still helping you feel covered, supported, and like yourself.
When Should You Measure for a Maternity Bra?
There is no single right moment, because every pregnancy has its own rhythm. Many women need a more accommodating bra by the end of the first trimester, when breast tenderness and early growth can make old favorites feel suddenly unforgiving. Others notice the biggest changes later in pregnancy.
If you are shopping for bras to wear during pregnancy, measure when your current bra starts feeling tight or uncomfortable. If you are shopping specifically for breastfeeding, consider measuring again around 36 to 38 weeks. At that point, your rib cage and breast size may be closer to where they will be just before delivery.
Still, plan for change after birth. When your milk comes in, your breasts can feel fuller for a few days or weeks. A stretchy, wire-free nursing bra, nursing tank, or bra-less nursing gown can be especially comforting during this transition because it offers gentle support without a rigid fit. At Aimee Nursing Gowns, we believe the pieces you wear during recovery should work with your body, not make you squeeze back into a pre-baby version of it.
Choosing a Size That Has Room to Change
Maternity and nursing bra sizing is a little different from choosing a bra for a body that stays relatively consistent month to month. Flexibility is often your friend, particularly if you are buying before delivery.
Look for soft, breathable fabric; adjustable straps; multiple hook-and-eye settings; and cups that stretch or accommodate changing fullness. If you are between sizes, the better choice depends on where you are in your journey. During pregnancy, sizing up in the band or cup may offer welcome breathing room. In the early postpartum days, a stretchier style may feel better than sizing far up in a more structured bra.
Underwire bras can work for some women during pregnancy and nursing, but comfort is personal. A properly fitted underwire should sit around breast tissue, never on it. If a wire presses, pokes, or feels uncomfortable as your breasts change, choose a wire-free option. Many moms find that soft support is exactly what they want for sleep, lounging, hospital bags, and tender early feeding days.
Signs Your Maternity Bra No Longer Fits
Your body will usually tell you when it is time to remeasure. A bra that once felt fine can become uncomfortable surprisingly quickly, especially during growth spurts or changes in feeding patterns.
You may need a new size or style if your band feels painfully tight, your breasts spill out of the cups, the straps constantly slip, or the center and sides of the bra press into breast tissue. Red marks that fade quickly can be normal, but deep grooves, numbness, chafing, or soreness are not something to simply tolerate.
Pay attention after your milk supply regulates, too. Some women need a larger bra immediately after birth, then a slightly different fit several weeks later. Keeping one or two flexible bras in rotation can make those changes feel much less disruptive.
A Note on Measuring During Pregnancy and Nursing
Try not to judge your changing body by your old bra size. Pregnancy and postpartum bring enough pressure without making a number on a tag feel like a verdict. A larger band, a fuller cup, or a softer bra style is not a setback. It is simply your body doing meaningful work.
The right maternity bra supports more than your breasts. It can make sleep less fussy, feeding more convenient, and long days feel a little gentler against your skin. Measure when you need to, choose comfort with confidence, and give yourself permission to adjust as often as your body asks.