What do Bra Sizes Mean?

What do Bra Sizes Mean?

Hey! You may know that here at Curvy Kate HQ we're a little mad on bra fitting, but not everyone has the knowledge or understanding of the bra fitting basics, so guess what? We're here to help! So if you've ever wondered to yourself 'What do Bra sizes mean?" then this post is going to explain everything and make sure you go away knowing exactly what you're looking for. Simples.

Ok so first things first - this is a bra size (Psst...click the size to shop):


It looks a little funny with it's mix of numbers and letters but there is no need to be scared - once you know what they mean it all makes sense- we promise!

The Number:

The number is always at the beginning and this refers to the back band and how many inches it measures. Back band measurement only come in even numbers and progress like this:

28, 30, 32, 34, 36, 38, 40, 42, 44, 46+

Knowing your back band size is the start to finding your perfect fit. To find out what you should be wearing- measure your underbust (horizontally around your rib cage under your boobs), making sure to hold the tape firmly. What you measure here indicates your back band size. If you measure an odd number then try the size on either side to see which fits the best. Remember - Your back band does 80% of the work when it comes to supporting you boobs so it needs to be firm fitting so it doesn't move.

Right well that's that sorted now on to...

The Letter:

The Letter that follows the number refers to the volume of the cup size. The order of cup sizes goes as follows**:

AA, A, B, C, D, DD, E, F, FF, G, GG, H, HH, J, JJ, K +

The tricky thing with cup sizes is that they aren't a definitive size, i.e. not all G cups are the same because it all depends on the back size they are teamed with. To quote our good friend Georgina from Fuller Figure, Fuller Bust, saying a cup size without a back size is like saying 'half past' when referring to the time but not giving the hour- It makes no sense without all the information.

So this is how it works: for every back size you increase, the relative cup size increases by the volume of one cup. Essentially a 34G is one cup size volume larger than a 32G.

And that's why you can never know how big a 'G' cup is without knowing the back size.

Another example is a 36D will be 2 cup volumes larger than a 32D.

A 30E will be 1 cup volume larger than a 28E.

A 40K will be 5 cup volumes larger than a 32K.

& so on!

Psst...you can use our Find My Size tab on our website to easily find all our bras in your very own size!

This then swiftly moves us on to Sister Sizing...

Sister Sizes:

So because increasing the back size can also change the volume of the cup, there is a way to ensure the the cup volume stays the same and only the back band changes, this is called 'Sister sizing'. See below an example in a diagram...

So, a 30E's sister size is a 32DD. We have gone up a band size, but down a cup size to keep the cup volume the same - if we went for a 30DD, the cup volume would be way too small. Remember, the band does most of the work in supporting your boobs!

So these sizes hold the same quantity of boob but the back size varies. It can be useful to know what your sister sizes are in case you need to increase or decrease your back size. (We strongly recommend booking in with one of our Virtual Bra Fitters to find out your size - then come back to this blog to find out your sister size or ask one of our fitters!) Here is a diagram showing how changing back sizes and cup sizes affect one another.

So there you have it, a quick guide to bra sizes and what they mean. It's not so hard understand is it?

So did you learn something new here? Do you now think you might be in the wrong size? If you have any questions then feel free to contact us via the comments below or on Twitter. Equally if you would like help from me, The Bra Whisperer®!

Big Love x

**Please note that this post refers to UK sizing methods and if you are unsure of international sizes then refer to our size guide below.

Size Chart Converter

Shop Our Instagram