US to UK Bra Cup Size Conversion
| US Cup | UK Cup |
|---|---|
Sizing conventions vary by brand and by cut — this table shows the standard published conversion. Always check the garment's own size chart when one is available. See how these tables are compiled.
Cup letters alone, without the band context, are an incomplete question
Asking how a US cup letter converts to a UK cup letter without also specifying the band size is a bit like asking how many centimetres an 'inch and a half' is without saying an inch and a half of what — cup size describes a volume relative to the band measurement, not a fixed absolute quantity, so the honest answer to 'what's my UK cup size' depends on your band size as much as your bust measurement.
Through A, B, C, and D, US and UK cup letters align directly regardless of band size, so this is the easier part of the range to convert. It's past D where mainstream US lettering (which has historically stuck with 'DD' and 'DDD' rather than expanding) and UK lettering (which continues into E, F, FF, G, GG, H and beyond) genuinely diverge, and where band size interacts with the conversion most.
Sister sizing is the real mechanism behind cup-size 'conversion'
Because cup volume is defined by the difference between bust and underbust measurement, the identical cup volume can be labeled with a smaller band and bigger cup letter, or a bigger band and smaller cup letter — moving one band size in either direction while adjusting the cup letter one step the opposite way keeps the represented volume roughly constant. This sister-sizing relationship is what lets you 'convert' a cup letter at all once band size is held fixed or adjusted.
UK specialty retailers offer more resolution above a D cup
Mainstream US bra brands have historically offered less lettered resolution above D than UK brands do, and UK specialty lingerie retailers in particular have built an entire product category around fuller-bust fitting with far more graduated cup letters than most American shoppers are used to seeing — worth exploring if your US cup letter has felt like an imprecise fit for years.
Getting the band-and-cup pairing right first
Specify your band size alongside your cup letter before attempting any conversion, use the sister-sizing relationship (one band size, one cup letter, in opposite directions) to explore nearby options, and check a UK specialty retailer's chart specifically if you wear a US DD or DDD and have never had a properly fitted alternative.
Frequently asked questions
Can I convert my US cup letter to UK without knowing my band size?
Not meaningfully — cup size describes a volume relative to band measurement, so the same cup letter on different band sizes represents different actual volumes. Always convert cup and band together.
Why does UK sizing have more cup letters above D than US sizing?
Mainstream US bra brands have historically stuck with 'DD' and 'DDD' rather than expanding, while UK sizing (and UK specialty retailers especially) continues with E, F, FF, G, GG, H and further letters.
What is sister sizing, in plain terms?
Moving one band size larger while dropping the cup letter one step (or the reverse) keeps the represented cup volume roughly the same — it's the mechanism that makes cup-letter 'conversion' meaningful once band size is factored in.
Should I try a UK specialty lingerie retailer if my US size has never fit well?
It's worth exploring, especially for a US DD or DDD — UK specialty retailers offer considerably more graduated cup-letter resolution above D than the mainstream US market typically does.
Is the US-to-UK cup conversion reliable through the A–D range?
Yes, that part aligns directly regardless of band size — the genuine complexity is concentrated above a D cup, where the two systems' lettering conventions diverge most.