Why US to UK conversion is mostly about cups
US and UK bra sizes use the same measuring logic. The band is the underbust in inches, and each inch of difference between bust and band adds one cup. That means US to UK conversion leaves the band alone and leaves most cups alone too. A US 32A is a UK 32A. A US 38D is a UK 38D.
The work starts above DD, where the US and UK name the same cups differently. The converter above handles it. This page explains what it is doing, so you can trust the result.
Bands stay the same
There is no band conversion between the US and UK. A 34 is a 34. If you see a different band number on a tag, it is probably an Australian or European number printed alongside, not a UK one. The bra size chart shows those systems side by side.
US cup names are less consistent
The UK has one fairly settled order: DD, E, F, FF, G, GG, H. US brands are less uniform. After DD you may see:
- DD or E for the same cup. Many US brands treat them as one size.
- DDD or F for the next cup. This is the cup the UK calls E.
- G, H, I for the cups after that. Some brands write DDDD instead of G.
So the most useful thing to know is this: after DD, US letters run one or more steps ahead of UK letters. The common pairs are:
- US DDD is UK E
- US G is UK F
- US H is UK FF
- US I is UK G
- US J is UK GG
If the US label is unusual, check what the brand means before converting. A brand’s own chart always beats a general rule above DDD.
Worked examples
- US 36DDD converts to UK 36E.
- US 34G converts to UK 34F.
- US 32H converts to UK 32FF.
- US 38DD stays UK 38DD.
Where people go wrong
The common mistake is assuming the letters line up all the way. Someone who wears a US G and orders a UK G gets a cup one step larger than she needs. A UK G is a US I.
The second trap is the US E. On many American labels it is just another name for DD, while the UK E is the next cup up. If a US tag says E, treat it as DD unless the brand says otherwise.
Buying from a UK brand
UK brands generally print UK sizes first and may show other systems on the same tag or chart. A practical routine:
- Start from a US size that fits well.
- Keep the band number.
- Convert the cup with the converter or the pairs above.
- Compare with the brand’s chart, especially above DD.
- Do a how a bra should fit when it arrives, and keep the tags on until it passes.
If the new bra fits the cups but not the band, try a sister size rather than another cup letter. If you need the reverse direction, see UK to US bra size.
Sources & method: sizing rules follow the standard band-and-cup system used by UK, US, AU and EU brands, checked against fitting guides from specialist retailers and fitting communities. How we work.