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US to UK Bra Size Converter

Estimate your bra size from underbust and bust measurements, or convert an existing size between US, UK, EU, FR and IT — plus its sister sizes.

Measure snugly (not tight) with a soft tape: underbust right beneath the bust, bust at its fullest point.

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Reading measurements
Matching sizes
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Result

This page opens the bra size calculator with the conversion direction already set to US-to-UK: type your US size, such as 34B, and the UK equivalent appears immediately, along with its two sister sizes.

Band numbers are the easy part here — US and UK bands both count in inches and use exactly the same numbers, so a US 34 band is a UK 34 band, no conversion needed. Cup letters are where the systems split: they match through D, but above that the US doubles letters (DD, DDD/F) while the UK uses single letters with occasional doubles at different points (DD, E, F, FF, G, GG, H) — so a US 36DD becomes a UK 36E, not a UK 36DD. The calculator applies this published equivalence table automatically.

The full calculator is available on this page, just preconfigured for this direction — switch it to UK-to-US, pick a different pair of countries, or measure a size from scratch instead of converting one. Every calculation happens locally in your browser with no uploads and no account needed.

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Accepted Formats & Rules

  • Traditional and modern band formulas from underbust, plus bust-minus-band mapped through an AA-to-L cup table.
  • Size conversion between US, UK, EU, FR and IT band numbers and cup letters, using real published band and cup charts.
  • Sister size calculator for whichever size you measured or converted: one band up/cup down, one band down/cup up.

Key Benefits

✓ Two modes in one tool: measure your size from underbust and bust, or convert a size you already know between five sizing systems.
✓ Cup letters are matched with a published international equivalence table, not a rough guess — with an honest note on where systems disagree.
✓ Every result also shows its two sister sizes — same cup volume, different band and cup letter — so you know what else to try.

Use Cases

  • • Never measured your bra size before and want a solid starting point before you shop?
  • • Ordering lingerie from a UK or European site and only know your US size?
  • • Curious what a US 34DD actually is in EU or French sizing?
  • • A brand is sold out of your size — want to know which sister sizes to try instead?