Bra Size Calculator - Calculator See


Bra Size Calculator

Calculate your accurate bra size using snug underbust and fullest bust measurements. Includes US, UK, and European size conversions and sister sizes.

Calculator Inputs

Measurement tape units.
in
Measure firmly around your ribcage directly beneath your breasts.
in
Measure loosely around the fullest part of your breasts, parallel to the floor.

Calculated Results

Recommended Bra Size
32C (US / UK)
Sister Size Down (Tighter Band) 30D
Sister Size Up (Looser Band) 34B
European Equivalent (EU) 70C
Values calculate live as you adjust inputs.

About Bra Size Calculator

The Bra Size Calculator determines your precise band size and cup volume by calculating the difference between your ribcage underbust measurement and fullest bust circumference.

What is Bra Size Calculator?

The Bra Size Calculator determines your precise band size and cup volume by calculating the difference between your ribcage underbust measurement and fullest bust circumference.

How to Use This Calculator

  1. Measure your snug underbust firmly directly under the breast tissue while exhaling.
  2. Measure your bust circumference around the fullest point of the bust while wearing an unpadded bra.
  3. Enter both measurements to see your recommended band, cup letter, and sister sizing.

The Mathematical Formula & Variables

Band Size = Underbust rounded to nearest even number (+2 if odd); Cup Letter = Bust - Band: 1 in = A, 2 in = B, 3 in = C, 4 in = D, 5 in = DD/E, 6 in = DDD/F, 7 in = G

Step-by-Step Worked Example

Scenario: Underbust measures 30 inches and fullest bust measures 35 inches.

  1. Snug underbust of 30 inches establishes a 32 band (standard modern snug fit).
  2. Cup difference = 35 - 32 = 3 inches.
  3. A 3-inch differential corresponds directly to a C cup.
  4. Recommended size is 32C. Sister sizes are 30D (snugger band) and 34B (looser band).

Result: Size: 32C (Sister Sizes: 30D, 34B)

Frequently Asked Questions

What are sister sizes in bra fitting?

Sister sizes have the exact same cup volume but different band tightness. If a 32C feels too tight in the ribcage, a 34B provides the same cup capacity with a looser band.

Why does the band provide 80% of support?

Bra straps only provide 10-20% of vertical support. A properly fitted, snug band anchored horizontally around the ribcage carries the majority of breast weight.