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How do maternity and nursing bra cup sizes work?


HELP! If a 34D is a slightly loose on the band but fine on the cup, what do I try next a 32D or a 32 E???

I’ve had this type of questions quite a few times over the last week or so, so I thought I’d go through UK bra sizing and how it works (or doesn’t!)

Well, lets start with what that 32 and 34 actually mean. When I first started fitting it though it referred to the actual size of the band of the bra around your ribcage. Obviously this isn’t quite correct, but it can be used as a guide. The bigger this number gets the wider the measurement around your ribcage just under your breasts, but the conversion is more like this:

You measure around your ribcage:
27-28 inches – Your band size will be 32 inches
29-30 inches – You band size will be 34 inches

Band Size – Measure around your ribcage in inches, then add 4 (called the Underbust +4 method) to get this

Cup size is a whole different matter, and widely different bras can have the same cup volume. We all know by common sense that someone boasting of a 36DD is going to have more breast volume than someone who has a 30DD, but why are the both called DD then? It’s because the cup letter only lets you know the difference between the underbust measurement and the full bust measurement. The result of this is that you get sister sizes – different band meaasurements but exactly the same cup volume…….

So these all have the same cup volume: 30F, 32E, 34DD, 36D, 38C, 40B
and so do these : 30D, 32C, 34B, 36A. Imagine being a 36A all your life and not knowing you breasts are actually the same size as a 30D !!!

And that’s where adjusting band sizes and cup together can get you a better fit of bra, because while cup volume isn’t adjustable on most bras, nearly all bra have band adjustments.

So if we’re considering the problem above where someone trying a 34D has a band that’s slightly loose but fine on the cup and they want to get a better fit, they should first try a 32E, because by going down a band size you need to increase the cup size to ensure the cup volume stays the same……

What about if the band is too tight but the cup is OK? Well use the same rule of thumb and when you go up a band size, decrease the cup size to compensate.

And if the band is OK and the cup doesn’t fit, just keep the band size steady and go up one cup at a time until your breast is fully enclosed by the cup, it doesn’t ride up and it doesn’t double boob.

I hope this makes sense and bras are no longer a mystery. Only men could invent such a complicated system……anyway you can find loads more tips on maternity and nursing bra fitting on the website :