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.
Processed entirely in your browser — nothing you enter here is ever uploaded.
Result
About this tool
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.
Example. An underbust of 30 in and a bust of 35 in produce the US size 34A, with sister sizes 32B and 36AA.
Limit. The cup index is clamped from AA through L, a bust that is not larger than the underbust is rejected, and convert mode accepts band numbers only from 20 to 60.