Bra Size Calculator
Measure your band (underbust) and bust, then get your bra size in US, UK and EU systems at once — plus a sister-size table for when a style runs small or large. Measure to the nearest ¼ inch while wearing a non-padded bra, arms relaxed.
TheCalculators — Bra Size Calculator
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Your Bra Size (US)
34C
Band 34" · Bust 37" · Difference 3"
- US / Canada
- 34C
- United Kingdom
- 34C
- European Union
- 85C
- Underbust (measured)
- 33 in
- Bust (measured)
- 37 in
- Cup Difference
- 3 in → cup C
Sister sizes (same cup volume)
Sister sizes keep the cup volume constant — useful when the band feels tight or loose but the cups fit well.
Studies estimate 70–85% of people wear an incorrectly fitted bra — most commonly too large a band and too small a cup. Sizes also vary between brands, so treat this as a starting point.
Most useful next
Formula
Band = underbust rounded to nearest even · Cup index = round(bust − band) (0=AA, 1=A, 2=B, 3=C, 4=D…)
- • Measure the underbust snugly → round to the nearest even number for the band size.
- • Measure the bust loosely over the fullest point.
- • Subtract band from bust and round: each whole inch of difference is one cup step.
Pro tips
- • Measure without a padded bra, standing straight with arms relaxed, tape level all the way round.
- • If the band rides up, go down a band size and up a cup (sister size).
- • EU band sizes count underbust in cm rounded to the nearest 5 (65, 70, 75…).
FAQ
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