Shopping for a UK A cup can involve more than choosing a cup letter, because bra size depends on both the band size and cup size. This guide focuses specifically on A cup bras, including how A cups change across different band sizes, which UK brands make A cup bras, how UK and international sizing compare, and how to confirm your correct starting size before buying.
Start by measuring your underband and bust and entering the measurements into our Bra Size Calculator. For step-by-step measuring and fit checks, see our Bra Fitting Advice. If you are comparing UK and international sizing or shopping across different brands, use the Bra Size Converter.
You can also see how A cup volume changes visually across different band sizes in our How Big Are A Cups? guide.
An A cup is only one part of a bra size. The complete size is made up of both the band size and the cup size, which means A cup volume changes as the band size changes.
In UK sizing, A sits between AA and B in the cup sequence: AA, A, B, C, D, DD, E, F, FF, G, GG, H, HH, J, JJ, K.
For example, a 30A, 34A and 40A all use the same A cup letter, but they do not have the same cup volume. As the band size increases, the corresponding cup volume also increases.
A UK A cup sits one cup size above AA and one cup size below B in the UK bra size sequence. Its overall volume depends on the band size it is paired with, so an A cup is not a single fixed breast or cup volume.
For example, a 30A has less cup volume than a 40A, even though both use the same A cup letter. Band size, body proportions and bra construction can also affect how an A cup looks when worn.
For a more detailed visual comparison across different A cup band sizes, see our How Big Are A Cups? guide.
An A cup sits between AA and B in the UK bra size sequence. The diagrams below compare these three cup sizes on the same 34 band, showing how cup volume increases while the band size remains unchanged.
On the same band size, each step in the cup sequence represents an increase in cup volume.
34AA
34A
34B
These simplified educational diagrams compare nearby UK cup sizes using the same 34 band so the change in cup volume is easier to see.
On a 34 band, 34A sits between 34AA and 34B in cup volume. The band size remains the same while the cup volume changes.
To compare A cups across more band sizes, visit our How Big Are A Cups? guide, or use the Bra Size Visual Comparison Tool to compare different UK bra sizes side by side.
How cup sizes work: Bra cup sizes are based on the difference between the underband and fullest bust measurements. As you move through the UK cup sequence, each cup step represents an increase in cup volume.
UK brands may use different cup-letter sequences at larger sizes, particularly where double letters such as DD, FF and GG are included. An A cup, however, remains a standard cup size within the UK sequence and sits between AA and B.
A cup bras are available from a range of UK lingerie brands. The brands below include A cups within their UK collections. The band and cup ranges shown are the wider size ranges offered by each brand; the A cup sizes specifically available are listed in the next section.
Size availability can vary by individual bra style and collection, so always check the product size options before ordering.
Based on the confirmed brand availability information above, these are the UK A cup sizes currently shown across the selected brands. Availability can vary by individual bra style and collection.
An A cup changes in volume as the band size changes, so choosing your complete band-and-cup size is important when shopping for bras. Use the guides below to go directly to recommendations and sizing information for your UK A cup size.
You can also browse the complete A Cup Bras by Band Size directory or use our Bra Size Calculator if you are not sure which band size to start with.
UK and US bra sizing systems use many of the same band numbers and early cup letters, but the cup sequences can differ as sizes increase. In UK sizing, A sits between AA and B.
A UK A cup is often labelled A in US sizing as well, but it is still important to check the sizing system used by the individual brand when comparing products internationally.
For a fuller explanation of how the two systems compare, see our UK vs US Bra Size Comparison Guide. You can also use the Bra Size Converter when comparing sizes across different brands and sizing systems.
In many cases, yes. A is commonly used as the same cup letter in both UK and US bra sizing.
The main differences between UK and US sizing appear further along the cup sequence, where the lettering systems begin to diverge. Even so, always check the sizing system used by the individual brand before ordering.
For a wider comparison of the two systems, see our UK vs US Bra Size Comparison Guide.
An A cup does not represent one fixed cup volume. As the band size increases, the corresponding cup volume also increases.
The cup letter remains A, while the overall cup volume increases with the band size.
30A
34A
38A
These simplified educational diagrams show how A cup volume changes across different band sizes while the cup letter stays the same.
A 38A has more cup volume than a 34A, while a 30A has less. This is why bra size needs to be read as a complete band-and-cup combination rather than by cup letter alone.
For more visual examples across the A cup range, see our How Big Are A Cups? guide or compare different sizes using the Bra Size Visual Comparison Tool.
These underwired A bras are available in UK sizing from established lingerie brands including Triumph and Freya. Underwired styles use a wire beneath the cups to provide structure and are widely available across A cup sizes.
Before ordering, confirm your starting size with our Bra Size Calculator and use our Bra Fitting Advice to check band, cup, wire and strap placement.
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Start by measuring your underband and fullest bust. Enter those measurements into our Bra Size Calculator to get a recommended UK starting size.
Once you have a starting size, use our Bra Fitting Advice to check the band, cups, wires and straps when trying on a bra.
If you are comparing equivalent sizes between brands or sizing systems, use the Bra Size Converter alongside the individual brand size guides.
For step-by-step fit checks and troubleshooting, see our Bra Fitting Advice. If you are comparing equivalent sizes across different brands or sizing systems, use the Bra Size Converter.
These non-wired A bras are available in UK sizing from established lingerie brands including Triumph and Glamorise. Non-wired bras, sometimes called wireless bras, do not use an underwire beneath the cups and are available across a range of A cup band sizes.
Before ordering, confirm your starting size with our Bra Size Calculator and use our Bra Fitting Advice to check band, cup and strap placement.
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Sister sizing can be useful when your usual size is unavailable in a particular style. Sister sizes use a different band size and cup letter while keeping a broadly similar cup volume.
If you move up one band size, you usually move down one cup size. If you move down one band size, you usually move up one cup size.
For example, 30B, 32A and 34AA are sister sizes because they have a similar cup volume but different band lengths. Sister sizing changes the overall bra dimensions, so it is best used as a comparison tool rather than treating the sizes as identical.
A common A cup sister-size example is:
These sizes have a similar cup volume but different band lengths.
30B
32A
34AA
These simplified educational diagrams show how sister sizes can keep a broadly similar cup volume while the band size and cup letter change.
Moving up a band size usually means moving down a cup size, while moving down a band size usually means moving up a cup size to keep a similar cup volume.
For a full explanation of how sister sizing works, see our Bra Sister Sizes Guide.
You can also use the Bra Size Visual Comparison Tool to compare sister sizes side by side.
If you want to explore A cup sizing in more detail, these related guides cover nearby cup sizes, visual comparisons, sister sizing and A cup availability across different band sizes.
Is A a small bra size?
A is a cup size rather than a complete bra size, so it cannot be described accurately as a fixed breast size on its own. Overall cup volume depends on both the band size and cup letter. For example, a 30A has less cup volume than a 40A, even though both use the same A cup letter.
What is the difference between AA and A cups?
In UK bra sizing, A is one cup step above AA and one cup step below B. On the same band size, an A cup therefore has more cup volume than an AA cup and less than a B cup. See our
AA Cup Bras guide
and
B Cup Bras guide
for nearby cup-size comparisons.
What does A mean in bra sizing?
A identifies the cup part of a bra size and sits between AA and B in the UK cup sequence. It must be combined with a band size, such as 30A, 34A or 40A, to describe a complete bra size.
Is a UK A cup the same as a US A cup?
In many cases, yes. A is commonly used as the same cup letter in both UK and US sizing. Differences between the two systems become more noticeable further along the cup sequence. See our
UK vs US Bra Size Comparison Guide
for more detail.
Does band size affect A cup volume?
Yes. A cup volume increases as band size increases. A 38A therefore has more cup volume than a 32A, even though both use the same cup letter. Our
How Big Are A Cups?
guide shows this visually across different band sizes.
What cup size comes after A?
In the UK bra size sequence, B comes directly after A. The sequence continues
AA, A, B, C, D, DD, E, F, FF, G and beyond.
For general background on bra sizing systems and cup-size terminology, see the bra size reference on Wikipedia .
