Introduction
Wearing the correct bra size significantly impacts comfort, posture, and support. Studies suggest that a large proportion of women wear the wrong size, often because sizing can feel confusing or inconsistent between brands and countries. This bra size calculator takes your two key measurements and instantly calculates your correct size across US, UK, and EU standards.
What This Calculator Does
Enter your bust (fullest part of the chest) and underbust (below the bust) measurements in inches or centimeters. The calculator determines your band size, cup size, and equivalent sister sizes.
Inputs Required
- Bust Measurement: The circumference around the fullest part of your chest
- Underbust Measurement: The circumference snugly around your ribcage just below the bust
- Unit: Inches or centimeters
Outputs Provided
- US Bra Size: Band size (number) and cup letter (A, B, C, D, etc.)
- UK / Australian Size: Equivalent in the UK sizing system
- EU Size: European numeric size equivalent
- Sister Sizes: Alternative sizes with the same cup volume
How the Calculation Works
Bra sizing has two components: the band (underbust measurement rounded to the nearest even number) and the cup (the difference between bust and underbust measurements).
Band Size = Underbust (in) rounded up to nearest even number
Cup Difference = Bust (in) - Underbust (in)
Cup Letter: 1" = A, 2" = B, 3" = C, 4" = D, 5" = DD, etc.
For example, if your underbust is 33 inches and your bust is 37 inches, the difference is 4 inches, which corresponds to a D cup. The band rounds up to 34. Your size is 34D.
How to Use the Calculator
- Select your preferred unit (inches or centimeters)
- Measure around the fullest part of your chest and enter the bust measurement
- Measure snugly around your ribcage just below the bust and enter the underbust measurement
- View your recommended size and international equivalents
Example Calculation
- Bust: 38 inches
- Underbust: 33 inches
- Difference: 5 inches = DD cup
- Band: 34
- Result: 34DD (US), 34DD (UK), 75DD (EU)
Real-World Scenarios
Online Shopping
A shopper buying lingerie from a European brand needs to convert her US 36C to the EU equivalent. The calculator provides the EU size immediately, reducing the chance of ordering the wrong size.
Post-Pregnancy Fitting
A new mother notices her pre-pregnancy bras no longer fit comfortably. Using the calculator with her new measurements helps her find the correct size for her changed body without a costly fitting appointment.
Sports Bra Selection
An athlete looking for a high-support sports bra uses the calculator to confirm her band and cup size, then uses the sister sizes feature to explore alternative band-cup combinations that might offer a better fit in the specific brand she prefers.
Understanding Sister Sizes
Sister sizes are bra sizes that share the same cup volume but have different band sizes. For example, 34D, 36C, and 32DD are sister sizes. If a 34D feels tight in the band but fits in the cup, try a 36C. If the band fits but the cup is too big, try a 32DD. Understanding sister sizes helps when your exact size is out of stock.
Common Mistakes to Avoid
- Measuring over a padded bra: Padding adds volume and produces an inaccurate bust measurement
- Pulling the tape too tight or too loose: The underbust should be snug but not compressing, the bust should be relaxed
- Using outdated add-inches method: The older method of adding 4 or 5 inches to the underbust is no longer the standard and often produces incorrect band sizes
- Ignoring brand variation: Sizing varies between manufacturers. Use this as a starting point and try sizes on when possible
Related Calculators
Try the Shoe Size Conversion calculator to convert footwear sizes across international standards, or the Height Calculator for converting between measurement units.