Nursing and Maternity Bra Size
During pregnancy and nursing your bra size can change, sometimes more than once and in both band and cup. Measure again whenever your bra feels tight or loose, use the calculator for a starting size, and choose stretchy, adjustable styles. For questions about your body, ask your midwife or doctor.
Measure for a maternity or nursing bra
The calculator needs JavaScript. Without it, use the steps and the size chart below: measure your snug underbust and your bust in inches, round the underbust to the nearest even number for the band, and count one cup letter per inch of difference.
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Your starting size
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Sizes vary between brands and styles. Use this as a starting point and try bras on: the band should sit level and feel firm on the loosest hook.
Next: sister sizes explained · convert to other countries · measuring tips
Why size changes
Both the ribcage and the bust can change during pregnancy and after birth, and size can go up and down again while nursing. Because these changes differ a lot between people, there is no reliable way to predict your size ahead of time. Measuring again when your current bra stops fitting is the practical approach.
Choosing a flexible fit
- Extra hooks: many maternity bras have several rows of hooks so the band can follow your ribcage.
- Stretchy cups: soft, stretch cups adapt to size changes during the day.
- Clips: nursing bras have clips on the straps so a cup can be opened with one hand.
- Comfort first: choose what feels comfortable. Ask your midwife if you are unsure what suits you.
Measuring tips
Measure at a time when you feel typical for that day. While nursing, size can vary across the day, so some people measure at different times and choose a stretchy style that covers the range.
Frequently asked questions
When should I buy a maternity bra?
When your current bra starts to feel tight in the band or cups. Measure again at that point, rather than at a set week, because changes come at different times for different people.
Will my bra size change after pregnancy?
It often does, and it can change again while nursing and after you stop. Measure whenever your bra stops fitting comfortably and use the calculator for a new starting size.
Can I use this calculator while pregnant?
Yes. It calculates a size from your measurements at that moment. Because your size may change, styles with extra hooks and stretchy cups give you more room to adjust.
Are underwire bras OK while nursing?
Many people choose soft, wire-free styles for comfort while nursing. If you have questions or concerns about underwire, ask your midwife, health visitor or doctor rather than relying on a website.
How should a nursing bra fit?
Like any bra: a firm, level band, cups without gaps or spilling, and clips that you can open with one hand. Stretchy cups help as size changes during the day.
Should I measure at different times of day?
While nursing, measuring at a couple of different times shows how much your size varies. Choose a size and style that is comfortable across that range.
Last updated: October 15, 2026