SuperCalX

Bra Size Calculator

Estimate your bra size based on band and bust measurements.
Calculator
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Analysis
Interpretation of the current calculator output

Enter values to see detailed analysis and insights.

How to Use

Step-by-step instructions
  1. 1Measure your underbust (snug, around ribcage).
  2. 2Measure your bust (fullest part).
  3. 3Enter the measurements in inches.
  4. 4The calculator will estimate your US size.

US Standard Sizing

Calculates band size by adding 4-5 inches to the underbust measurement (standard US method), then determines cup size by the difference between bust and band.
Cup = Bust - Band

Variables:

BandUnderbust + 4/5 inches
Cup1" diff = A, 2" = B, etc.

Example

30" Underbust, 35" Bust

Inputs:

Underbust:30 inches
Bust:35 inches

Steps:

  1. 1.Band = 30 + 4 = 34
  2. 2.Diff = 35 - 34 = 1 inch
  3. 3.1 inch = A Cup
Result:
34A

Frequently Asked Questions

Why +4 inches?

This is a traditional sizing method used by many US brands. Some modern fitting methods use the underbust measurement directly as the band size (e.g., 30" = 30 Band), which would result in a larger cup letter (e.g., 30DD).

What are sister sizes?

Sister sizes are bra sizes that have the same cup volume but different band lengths. If a bra fits in the cup but is too loose/tight in the band, try a sister size.