Calculator
Get your bra size in 30 seconds
Calculator
Bra Size Calculator
Enter your measurements to get your bra size, with instant conversions and sister sizes.
Instant starting size
34D
How to measure
- Step 1: Measure around your ribcage under the bust.
- Step 2: Measure around the fullest part of your bust.
- Step 3: Use both numbers as a starting point, then check the fit.
Looking for Australia or New Zealand sizing?
Use the AU calculator if you want your result shown in the bra size system used in Australia and New Zealand, with cm measurements kept easy to enter.
Australian bra size calculatorNew Zealand bra size calculatorBetween sizes?
If one band feels too firm and the next feels loose, compare nearby sister sizes. They adjust the band and cup together so you can test a similar cup volume with a different band feel.
Try sister sizesWhat your result means
Band number
The band is the number part of the size. It should feel firm around your ribcage and stay level instead of sliding upward.
Cup letter
The cup letter is relative to the band. A cup letter on one band is not the same volume on every other band.
Check the fit before you trust it
- The band should stay level across your back when you lift your arms or sit down.
- The cups should not spill, wrinkle, or leave a hard gap at the top edge.
- If the cup feels close but the band feels wrong, compare the nearest sister size.
- If you have pain, post-surgery needs, pregnancy or nursing changes, use a professional fitting as well.
FAQ
How does the calculator estimate a bra size?
It rounds your underbust to a nearby even band and maps the bust-to-band difference to a cup step. Treat the result as a starting point, then check the real fit.
How accurate is an online bra size calculator?
An online calculator can point you in the right direction, but it cannot see shape, fabric, wire width, or brand differences. Always use the result with a fit check.
What if I am between band sizes?
Try the closest band first, then compare the sister size up or down. A band should feel firm and level without painful pressure.
What is a sister size and when should I use one?
A sister size changes the band and cup together to keep a similar cup volume. It helps when the cup feels close but the band feels too tight or too loose.
Why is my UK bra size different from my US size?
Cup lettering is not identical across sizing systems, especially after D. Use conversions as a guide and check the brand size chart before buying.