Calculating Bra Cup Sizes?

You would think that determining bra cup sizes would be easy but as all ladies quickly find out, it is not. Not only does it differ from country to country, like all women's clothes, it differs by manufacturer in that country.

Explaining Sister Sizes in bras

You can understand why retailers pressurise clothing manufacturers to do vanity sizing. With the pressure of media we are all acutely figure conscious but surely for bra sizes that should not be the case?

Oh and there is a simple explanation of the term sister sizes below too.

Before I start, I would like to clarify one possible confusion. 'Plus size' bras are not the same as 'full bust' bras.

Plus size bras refer to a large band size, for example 44C. Full bust bras relate to a large cup size, for example 34G. I am principally discussing large cup bras.

Below I discuss the two simple measurements required every time, then I move onto the international variation in bra cup sizes.

Just remember, it is band size and cup size.

If however you are looking for instructions on how to work out your own size, click here for how to measure a bra.

A Simple Explanation Of
Bra Cup Sizes

Whenever you see a brassiere measurement it is always something like 34DD, 36F. That is a number, followed by a letter(s). The first is the band measurement, the 'strap' that goes all the way around your chest; the second is the cup dimension, in which your breasts sit.

I should say immediately that both the British and American markets use imperial measurements for band sizes, ie inches, (but more of that below).

Goddess Keira Large cup braUp to 46H
Goddess Adelaide Bra34H Goddess

The band size is measured at that point just beneath your bust. Of course logically a band size should equal your actual dimensions, but sometimes it does not, again that is explained better in how to measure a bra size.

The cup is the material, (often shaped like a triangle) which your boobs are placed in. The smallest cup size is an AA it then gets progressively larger up to the seriously big cup sizes which this site primarily caters for.

Bra cup sizes are traditionally dictated by the difference between the measurement around your under-bust and your bust itself. Every inch bigger your bust is than the under-bust, is one inch bigger in cup size. Hence one inch is A, two inches B etc.

Sister Sizes

Sister sizes is a relatively new phrase but I think it sums up the following issue really well. There is a common misconception that bra cup sizes tend to be the same, for example a 34E is similar, if not the same, as a 30E. This is simply not the case.

Rebecca Bra by Fantasie30E Fantasie
Deco Delight Bra by Freya32FF Deco

Simply put, as band sizes increase, or decrease, the cup sizes changes. For example, a 32E , is actually the same cup - or more technically volume, as a 30F. 

This may seem odd at first but the band size makes a difference. A 30 band size is just that bit shorter, than a 32 in the sister sizes, if you lay a bra out flat on a table. Likewise a 34 band size bra is just a little longer again than a 32.

It is not only length. The depth of the band size increases or decreases accordingly. So for example, the depth of a 30 band size bra, may be a tad less than a 32 band size. What effect does this have? Well, a slightly deeper band will naturally have a matching, slightly bigger cup.

I know a string of numbers can look boring and meaningless, but bear with me because it is the best way of explaining this.

A 28G = 30FF = 32F = 34E = 36DD = 38D. (Remember, for some wacky reason, many manufacturers do not do a EE). This explanation can take some while to register because it seems so illogical but once you get it, it makes you understand better why it is so difficult to define what big boobs are. 

....and that ladies, is sister sizes!

It brought it home to me some while ago when I was chatting with a decidely busty friend at a zumba fitness class and she confided that she wore a 36FF. I had naively assumed she would be a far bigger cup size but 36FF = 34G = 32GG = 30H. 

Calculating bra cup sizesArmona form $22
Gaia from £12

International Bra Cup Sizes Variation

Like so much else to do with clothes sizing, there is no international system of brassiere sizing, however some countries do use the same calculations. There is of course two elements in bra measurement, cup and bra sizes and these two also can vary by country.

The whole concept of cup and band sizes only started in the 1930's as brassieres gradually emerged from their fore-runners, the corset.

Cup Sizes for Big Bras

The UK and USA both use an imperial system, even though the UK went metric in the Seventies. Australia & New Zealand adopt a similar classification whereas the Europeans naturally enough, use a metric system.

Why oh why can we not have a standard cup sizes system? Oh well another dream that will never happen.

UK Bra Cup Sizes

For cup sizes for big bras in the UK we go:

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

Note the anomalies: the fact that a double size is usually bigger, so why is a double AA smaller than an A? Why no double B, C or E? When we have AA, DD and FF. Note also we miss out I, it is a bit like some high-rise buildings missing out a floor 13 because they think it is unlucky.

As you can see it is not exactly science, it is based more on historical sizing methodology and to someone looking at this afresh - it is plain daft.

UK cup sizes and US cup sizes have different classifications

American Bra Cup Sizes

To make life complicated for American women, the US uses two (or more) bra measuring systems. The main system is similar to the UK for cup sizes for big bras: A, B, C, D, DD, DDD, G, H, I, J, K, L, M, N, O.

Note that, unlike the UK, there is an I, but no E or F.

Some times the DD & DDD above are replaced by E and F - which is by far the most logical system

The second American system of bra sizing drops the DD and DDD and replaces them with E and F. This is by far the most logical system. Hence you have A, B, C, D, E, F, G, H, I, J, K, L, M, N. This classification does not have large sequence double letters. So the alphabet goes further.

There is even an attempt to start another classification, which runs:

A, B, C, D1, D2, D3, D4 etc.

I can only imagine the reaction of being classified as either 36D7, or 36DDDDDDD. Who ever came up with that one was clearly not a big busted woman.

Bra sizes vary internationally

Australia, New Zealand and South Africa:

Also follow the UK classifications but then diverge for band sizes.

Europe:

European countries all used to have different systems again but thankfully when they created the 'European market' they introduced a new standardised Euro-wide system. That of course, is metric.

The bra cup sizes run (like the second US system): AA, A, B, C, D, E, F, G, H, I, J. Note this too includes the letter I. (Japan also follows that system.)

The only complication is that this is Europe and so whilst people are meant to do things a certain way, not everyone has adopted the 'new' sizing system and older bras can still have the 'old' national sizing method.

I have only really discussed the English speaking world and Europe as that is the language of the website. Apologies if I have left out your country but my language skills are pitifully restricted.

Band Sizes:

Thankfully band sizes tend to have more consistency internationally. Band sizes are the same in the UK, USA and South Africa. The Euro system follows the same logic but is naturally different being metric.

Australia used to follow the UK / US system but some 10-20 years ago decided the UK / US system was daft and moved to a dress size system, 8, 10, 12, 14, 16, 18 etc. Who can say if either methodology is better or worse? Thankfully New Zealand followed Oz, so there is some unity in that part of the world.

International cup sizes can be confusing

How confusing is all of this? But at least we do not have Cyrillic lettering or Chinese characters! I will do more research on other countries when I have time but if anyone can help me out by educating me on the bra sizing used in their country, or region, then please do.

  • To return to the top of the page, click large bra cup sizes
  • Conversely if you are more interested in the different types of bra and the best and worst styles for big busted women, go to the main page: big bras
  • For more general clothing related issues for the generously endowed, head back to the Home page, clothes for large breasts.



Did you like this page, did you learn something, maybe it reinforced you own views? I want to give as much (hopefully helpful) advice to the busty sisterhood as I can.

Please remember, we are all different. You may like to wear certain clothes and styles which I am suggesting that you should not. That is your absolute right. Do what makes you feel good. This site undeniably goes for the more modest approach because I feel all busty ladies already know how to be more racy if they wish.

It would really help me improve the site profile if you would click the Facebook 'Like' button. Pretty please! Susan

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Large cup bra sizes can be confusing


Cup Sizes For Big Bras

A fabulous old advert for different cup sizes - as long as you stop at a D cup!

An early example of an advertisement showing bra cup sizes. Of course A- D only!

Yes ladies - you now live in a more enlightened age.

One of the first bra (as we know it) patents from 1914.

An early bra patent


How do you compare
British & American bra sizes?

The short answer is - not easily. There are a number of sizing systems but the most common ones are below.

       UK         US

  • AA         AA
  1. A           A
  2. B           B
  3. C           C
  4. D           D
  5. DD         DD
  6. E           DDD
  7. F           G
  8. FF          H
  9. G           I
  10. GG         J
  11. H           K
  12. HH         L
  13. J           M
  14. JJ          N
  15. K           0

Confused. I would be amazed if you weren't.

Add in the annoying fact that different brands vary in sizes and the fact that breast shape can make a difference too and we have an almighty level of confusion.


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Susan