In UK bra sizing, A is one cup size larger than AA, and B is one cup size larger than A.
The cup sequence around these sizes is: AA → A → B → C → D.
Cup size is not a fixed volume on its own. Cup volume changes with band size, so a 30AA, 30A and 30B increase in cup volume on the same band, while the same cup letter also represents different volumes across different band sizes.
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Compare any three UK bra sizes in the AA, A and B cup range.
The table below shows how AA, A and B cup sizes compare within the UK bra sizing sequence when the band size remains the same.
| Cup Size | Position in Sequence | Relative Cup Step |
|---|---|---|
| AA | Before A and B | Smallest of these three cup sizes |
| A | Between AA and B | One cup size above AA |
| B | After AA and A | One cup size above A |
These comparisons apply when the band size remains the same. Cup volume also changes as the band size changes, so an AA, A or B cup is not a fixed volume on its own.
The diagrams below compare 34AA, 34A and 34B using the same 34 band size. Keeping the band size the same makes it easier to see how cup volume increases through the UK sequence from AA to A to B.
These are simplified educational diagrams designed to show relative cup-volume progression when the band size remains the same.
When the band size remains the same, cup volume increases through the UK cup sequence. A 34A has more cup volume than a 34AA, while a 34B has more cup volume than both.
You can explore these sizes in more detail in our Best Bras for 34AA, Best Bras for 34A and Best Bras for 34B guides.
In the UK bra sizing system, AA, A and B are consecutive cup sizes. A sits directly between AA and B in the UK cup progression.
AA → A → B → C → D → DD
When the band size remains the same, cup volume increases as you move through the sequence from AA to A to B. This means A is one cup size larger than AA, while B is one cup size larger than A.
Further along the UK cup-size sequence, the progression reaches C and D before moving to the double-letter size DD. Other double-letter cup sizes, including FF and GG, are also used later in the sequence. These create additional steps within the cup-size progression. For a more detailed explanation, see our Double Cup Bra Sizes Guide.
You can explore the complete UK cup progression in our UK Bra Cup Size Chart.
Remember that cup volume also changes with band size. If you are moving between band sizes while keeping a similar cup volume, see our Bra Sister Sizes Guide or use the Bra Sister Size Calculator to compare equivalent-volume sizes.
Cup size is not a fixed volume. For example, a 32A, 36A and 40A all have different cup volumes because cup volume increases as the band size increases.
The same cup letter represents different bust measurements at different band sizes. The examples below show the measurement pattern used in this guide for AA, A and B cup sizes as the band size increases.
| Band Size | AA Cup | A Cup | B Cup |
|---|---|---|---|
| 32 | 32" | 33" | 34" |
| 34 | 34" | 35" | 36" |
| 36 | 36" | 37" | 38" |
| 38 | 38" | 39" | 40" |
If you want to explore AA, A and B cup sizes in more detail, or compare them with the neighbouring cup sizes in the UK sequence, use the individual guides below.
Cup letters do not represent a fixed volume on their own, because cup volume changes as the band size changes. You can explore AA, A and B cups across different UK band sizes using the guides below.
Yes. In the UK bra sizing system, A comes directly after AA. When the band size remains the same, A is one cup size larger than AA.
Yes. B comes directly after A in the UK cup size sequence. When the band size remains the same, B is one cup size larger than A.
The next cup size after B in the UK bra sizing system is C. The sequence around these sizes is AA → A → B → C.
If you are unsure which bra size to start with, measure your underband and fullest bust and enter your measurements into our Bra Size Calculator.
You can then check the fit of your bra using our Bra Fitting Advice, compare international sizing systems with the Bra Size Converter, or explore equivalent-volume sizes with the Bra Sister Size Calculator.
If you want to compare bra sizes visually, use our UK Bra Size Visual Comparison Tool to compare sizes across the full UK size range.
For additional background on how bra sizing systems developed, you may also find this bra size overview useful.
