This nursing bra size calculator helps expectant and new mothers find their correct bra size for comfortable breastfeeding. It uses standard bra sizing measurements to deliver accurate US, UK, and EU size equivalents. Use it when shopping for nursing bras to avoid ill-fitting, uncomfortable options.
Measure while wearing a non-padded, unlined bra for the most accurate results.
How to Use This Tool
Start by selecting your preferred measurement unit (inches for US/UK sizing, centimeters for EU sizing). Enter your underbust measurement (taken just below your bust, around your ribcage) and your bust measurement (taken around the fullest part of your breasts). Click Calculate Size to view your results, including band size, cup size, and international equivalents. Use the Reset button to clear all inputs and start over, or Copy Results to save your size details to your clipboard.
Formula and Logic
The calculator uses standard bra sizing conventions for accurate results:
- For inch-based measurements: Band size is your underbust measurement rounded to the nearest even number. Cup size is determined by the difference between your bust and underbust measurements, where every 1 inch of difference equals one cup size (1" = A, 2" = B, etc.).
- For centimeter-based measurements: Band size is your underbust measurement rounded to the nearest 5cm increment. Cup size is determined by the difference between your bust and underbust measurements, where every 2.5cm of difference equals one cup size.
- International conversions follow standard sizing mappings: US/UK band sizes align for measurements up to DD, with UK using E/F for US DD/DDD. EU sizes use centimeter-based band increments and a 2.5cm per cup size standard.
Practical Notes
Nursing bra sizing has unique considerations for everyday lifestyle use:
- Measure in the third trimester of pregnancy, as ribcage expansion and breast growth can change sizes up to 1-2 cup sizes.
- Always measure while wearing a non-padded, unlined bra to avoid overestimating bust size.
- Size up 1 cup size from your calculated result to accommodate milk production and breast engorgement during breastfeeding.
- If between band sizes, choose the larger option to avoid tightness around the ribcage, which can restrict breathing and milk flow.
- Nursing bras with adjustable straps and stretchy bands are ideal for fluctuating breast sizes in the first 6 months postpartum.
Why This Tool Is Useful
Ill-fitting nursing bras can cause discomfort, clogged milk ducts, and reduced breastfeeding confidence. This tool eliminates guesswork when shopping online or in-store, saving time and money on returns of poorly fitting options. It caters to both US/UK and EU sizing standards, making it useful for international shoppers. The detailed breakdown includes fit notes specific to nursing needs, which generic bra size calculators often omit.
Frequently Asked Questions
Should I measure before or after giving birth?
Measure in the third trimester (weeks 28-40) for the most accurate pre-birth size. Breast size will fluctuate in the first 6 weeks postpartum, so re-measure once your milk supply regulates for a better fit.
What if my bust measurement is exactly the same as my underbust?
A 0 inch/cm difference corresponds to an AA cup size. For nursing, you may still want to size up to a A cup to accommodate initial breast changes after birth.
Do nursing bra sizes run small?
Many nursing bras have slightly smaller fits than regular bras due to added support for breastfeeding. If between sizes, always choose the larger option, especially for band size.
Additional Guidance
When trying on nursing bras, ensure the band sits parallel to the ground and does not ride up your back. The cups should fully enclose your breasts without spillage or gaping. Look for bras with easy-access clasps that can be opened with one hand, a key feature for feeding on the go. Replace nursing bras every 3-6 months as elastic wears out and breast size continues to change during the breastfeeding journey.