• Here you will find all sorts of advice and updates of your bras and lingerie.

    Geraldine x

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Bra Size Measurement System


How do bra sizes actually work ?

The two important things to remember in bra sizing are:

1.  The band size is NOT your chest measurement (although it is related)

2.  The cup size is NOT the actual physical size of your boobs – it is a size relative to your chest measurement (Confusingly this means that not all D cups are the same size – so a 36D has a larger cup than a 34D).

I will provide a separate article with a bit more detail on how to measure your bra size – what I would like to do here is describe the sizing system.  Please Note:  this applies to the UK sizing system only.

The band size

The band size is related to your underbust measurement.  This is your chest measured where your bra band would sit (with the tape held as firm as your bra would be).   Once you have your underbust measurement) you add 4″ (if the measurement is even) and 5″ (if the measurement is odd).

I am really not sure how this system developed as it is very confusing – but that’s just the way it works.


–  a 33″ or a 34″ underbust measurement will result in a  38″ band size; and

–  a 35″ or a 36″ underbust will result in a 40″ band size.

Quite why the band size is not the same as the underbust measurement is beyond me – it would make things so much simpler, and easier to understand.

The cup size

The cup size is a measurement based on your overbust measurement RELATIVE to your band size.  Your overbust measurement is your chest measurement measured around the fullest part of your boobs with a comfortable bra ON.  Once you have your overbust measurement you compare it to the band size.


– If the overbust is the same as your BAND SIZE (not the underbust the band size) then you are an A cup

– If the overbust is 1″ larger you are a B cup

– If the overbust is 2″ larger then you are a C cup

… and so on

remember the UK cup sizing system runs in the following order:


Giving a complete cup size conversion table as follows:


Overbust vs Band Size


















Band Size



















Of course what this means is that someone with a:

– 34″ band and a 35″ overbust will be a B cup (34B),

– 36″ band and a 37″ overbust will be a B Cup (36B),

– and a 38″ band and a 39″ overbust will be a B cup (38B).


in each of these cases the actual physical size of the breast is not the same, and increases so a 38B breast is one size larger than a 36B breast which is one size larger than a 34B breast.



Its all very confusing – but I hope this guide has provided a little more clarity on what seems like an overly complex measuring system.


You really do need to understand your measurements on an on-going basis as very few of us will keep the same bra size throughout our lives – even though many ladies will try to wear the same sized bras !!


Geraldine x



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