What is my UK cup size? How to calculate the bra cup size…

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You might have some idea of what cup size you are. Or you might have no idea at all. Without knowing your band size there’s really no telling what your cup size is. Read more

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How do you know your cup size is A, B, C, or D?

women with measure tap cup size

Choosing a cup size always starts with determining your bra band size first.

See my bra calculator or visit

Bras and Size charts
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Let me give you an example.

Remember that bras 75A and 75B have different cup volumes. And bras 75A and 80AA have the same cup volume.

So if you wear 75B but find the band a bit too tight and cups just fine, you should try 80A instead.

Which cup is bigger?

different bras illustrating which cup size is bigger

The bras 90C, 95B and 85D all have the same cup volume.


Yes, they have. Bras with different numbers can have the same cup volume. It’s called sister sizes.

What does my example tell you?

Always start by finding the right bra band size

As bras with different band sizes can have the same cup volume, it’s a first to get that band right.

Another example.

A woman measures her bra size 36C. However, the band may feel too tight or a bit too loose.

If she’s happy about the cup size, she wouldn’t need to change this, wouldn’t she?

In this case, she simply goes up or down a band. But to keep the volume of her cup size, she has to change the cup number as well.

Taking a wider band will automatically change the cup volume as well.

So to keep the same cup volume she would choose:

  • band size down? – up a cup size – 34D
  • band size up? – down a cup size – 38B

Other articles you might like

Guide how to measure your bra size
How often does a bra size change?
The average UK bra cup
Determine your best bra band size
Small bra size chart AAA-B
UK bra size chart
Why is my bra hurting me?
Buying my first bra
6 Strapless bras for girls and teens
How to do the measurements at home

See my bra calculator or visit

Bras and Size charts
M&S UK | M&S IR | M&S US | First Bras