How to Calculate Bra Size
What is Bra Size?
Bra sizing uses under-bust for band size and bust-minus-band difference for cup. Studies suggest ~80% of women wear an incorrect size.
Formula
Band size = Underbust circumference (inches), rounded to nearest whole; Cup size = Overbust − Underbust (each 1" = 1 cup size; A/B/C/D/DD/E/F...)
- UnderbustIn
- Underbust circumference (Inches)
- OverbustIn
- Overbust circumference (Inches)
- Diff
- Overbust − Underbust (Inches (cup size))
Step-by-Step Guide
- 1Band (US/UK): round under-bust up to nearest even inch
- 2Cup: 1" diff = A, 2" = B, 3" = C, 4" = D, 5" = DD
- 3Sister sizes share same cup volume (34C = 32D = 36B)
- 4Measure bra-less at end of day
Worked Examples
Input
Under-bust 34", full bust 38"
Result
Band 34; cup D → 34D
Frequently Asked Questions
How do I measure correctly?
Underbust: snug around rib cage, directly under bust. Overbust: loose around fullest part of bust. Wear unpadded bra. Measure 2–3 times for accuracy.
Why do cup sizes vary by band?
Cup size is relative to band. 32D vs 36D have different absolute volumes (36D is larger). Sister sizes available: 34C = 32D = 36B (same volume, different band).
Should I get professionally fitted?
Yes, especially first time. Specialty lingerie shops train fitters. Many people wear wrong size (band too loose, cups too small common). Proper fit changes comfort/health.
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