Bra Fitting Guide

How to order the right bra band size from Lux and other UK brands:

Measure firmly around your rib cage, directly underneath your breasts in inches. The tape measure should be horizontal around your body and should not drop in the back. This is your underbust  measurement THIS IS NOT YOUR FINAL BAND MEASUREMENT FOR UK BRAS.

Add four inches onto your underbust measurement to get the band measurement. So if your underbust measurement is around 28” you’ll be needing a UK size 32 bra. 

This four inch oddity dates back to when bras were made from non-stretchy fabric which had to be cut large enough to accommodate your expanded ribcage when you raised your arms or did cartwheels across the kitchen. So in the case of your 28” underbust, they guessed that 4 inches of ease would make sure you didn’t rip the bra or break a rib during the course of the day. (If you want to be really exact you can try and measure your own expanded ribcage size, because what ever bra band you buy it needs to be able to go up to this size without pinching and cutting you)

These days we use power-mesh on our bras that expand the four inches as we move  but in the UK we are still left with the out-of-date size names. To make matters worse there is no universal agreed size for what those bands actually measure now that we are using powermesh. Within most mass market brands you can get a wide variation in band sizes depending on design, which makes for really complicated guess workwhen you are trying to buy a new bra.

So at Lux we’ve invented a bra band calibration table that takes the guess work out. It’s got three sets of measurements – unstretched bra, actual underbust, and fully stretched/ expanded underbust.

Firstly the unstretched measurement is something you can use if you already have a bra that fits you perfectly.  Measure that bra between the hooks at one end and the nearest set of loops at the other, like this.

Just measure up to the nearest loops  - in this case it's 23". Different bras have different amounts of loops on the end and they are just their to give extra adjustment.

It's really important to measure like for like - if you want to buy an underwired balcony bra then measure one that you already have that fits. Measurements for other types of bra will give different results as they mat sit lower down the ribcage and therefore be smaller or be a sportsbra that is built bigger to allow you to move.



This 32" bra measures 23" unstretched between the hooks at one end and the nearest set of loops on the other. 

Now stretch the bra to about how much it’s stretched when you wear it (not full stretch because you still need to be able to move about in it remember, so we’ll call this comfy stretched) this is equal to your underbust measurement at rest, measure again between hooks and loops, like this

Here's a comfy stretched size 32 bra below an unstretched size 32. Comfy stretched measures 28" up to the first loops

Lastly note the fully stretched measurement – this is what will give you the freedom to actually move in the bra when you're doing cartwheels across the kitchen and is also your actual underbust measurement during your most extreme movements or when taking deep breaths. The fully stretched measurement of a bra needs to be the same or slightly bigger than your fully expanded ribcage.


Now compare your results with our Lux charts

Bra unstretched measurement

23” – size 32 band

25” – size 34 band

27” – size 36 band


Your underbust measurement at rest and/or comfy stretched bra measurement

28” – size 32 band

30” – size 34 band

32” – size 36 band


Fully expanded rib measurement and/or fully stretched bra measurement

32” – size 32 band

34” – size 34 band

36” – size 36 band


Cup sizes ares named alphabetically e.g. A, B, C… and relate to the volume of the cup in relation to the band size of the bra. The theory is that if your bust measures 1" larger than your underbust then you are an A cup. If you think about  this for a moment you can see the problem - we can not tell volume of a round boob by measuring straight across with a tape, I've measured boobs that are a C cup, but that only stuck out 1" from the body. And since boobs come in all sorts of shapes and sizes with fullness above or below the nipple when we approach cup size armed with only a tape measure then we are really only guessing. In practice most women have an idea of their cup size and we can use the bras they already have that fit to come up with a very good estimation, even if those sizes appear different at first. Here's why - cup sizes are always relative to the band size, so a 32D cup is completely different to a 36D cup, in fact it's 2 sizes smaller. But a 32D cup is equal to a 34C cup and a 36B cup like this 32D = 34C = 36B - these are called sister sizes, they are same volume cup but on a different band sizes.

Most women have a collection of bras like this - different band sizes but that ultimately have the same volume cup.

So to order your Lux bra, first get the band size right using the tables above, then you can use the sister size table below to figure out what cup volume works best for you.


30 32 34 36 38 40 42 44
30C 32B 34A          
30D 32C 34B 36A        
30E 32D 34C 36B        
32E 34D 36C 38B      
32F 34E 36D 38C      
34F 36E 38D 40C    


It's worth pointing out that this is a really simplified version, for example, yes those sister sizes are equal volume but they are placed differently on the band - 30E will have hardly any space between the underwires at the centre front whilst it's sister 36B will have quite a gap between the wires. And what about the DD type volumes? Well, they are simply an E volume on a D wire, so the same volume as an E, but projecting out in such a way that they only have a D footprint if you like.