Bra Size Calculator

Estimate US bra size from under-bust and bust measurements, with UK/EU conversions.

Calculator Numbers & Math Updated Apr 20, 2026
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How to Use
  1. Measure under-bust (snug ribcage) and bust (fullest part).
  2. Result shows US/UK/EU band + cup sizes.
Measurements
Size

Method

Band
round under-bust to nearest even number (in)
Cup
bust − band difference → AA (0"), A (1"), B (2"), C (3"), D (4"), DD (5")…
Note
sister sizes exist — a poorly fitting band may warrant going up/down one size

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