Sister Sizes, Unlocking the Mystery of Bra Sizes

Sister Sizes, Unlocking the Mystery of Bra Sizes

November 01, 2017

Boobs are a minefield.

Most women don’t know their actual bra size (85-90%) & most women have been incorrectly told their size. Few have been told that their size will change dependent on the brand of lingerie & the style of bra, eg plunge v balcony.

Few of us talk about how one of our boobs is bigger than the other, or our nipples look different to each other or that some of us have more or less separation between our two breasts. Difference is normal when it comes to boobs! We’re here to put you on the straight and narrow when it comes to sizes.

Have you heard of Sister Sizes?

Ever wondered why you were fitting into a 34E in one shop, then you were measured in another and they landed the bombshell that you were in fact a 30FF – with no explanation how you could have changed sizes so substantially?!

You hadn’t infact changed – the bra cups are the same!

A 34E is the sister size to a 30FF.


The band size gives a measurement in inches in the UK – eg a 30, 32, 34 etc. These is an actual measurement around your underbust area.

Your cup size, eg D, DD, E is not a measurement, it’s a ratio. When the bra measuring system was originally invented, each letter stood for how many inches difference there was between your underbust and your widest part of the bust (usually the nipple). A for 1 inch, B for 2 inches, C for 3, D for 4, DD for 5, etc.

Your bra size actually stands for a volume, not a set number of inches/centimetres!

So for our co-founder, Fleurette. She was measured as a 32E by a high street chain, but she is in fact a 28FF – the same volume as a 32E however the 28FF fits her underbust correctly giving her the right support that she needs. Her sister sizes are:

32E | 30F | 28FF

Same as our co-founder, Alice. She was once measured as 34FF and a 36F – but is in fact a 30GG! Her sister sizes are:

34FF | 32G | 30GG | 28H

Who saw our Halloween pumpkin post – ‘guess the pumpkin’s bra size?’!

The bras shown were actually a 34DD and a 30FF however the volume of the pumpkins were equal to many sister sizes!

So for the 34DD one, the sister sizes were:

32E | 30F | 28FF

For the 30FF one, the sister sizes were:

28G | 32F | 34E

Ladies, if you’re wearing a 36E and you wear a size 8-10, it’s more likely that you’re in fact a 28GG, 30G or 32FF! Come to us, book a fitting, and we’ll make your boobs sing with uplift, and make you feel the very best version of yourself!

So remember,

Sister sizes: These bras have the same cup volume. As band size increases, bust letters decrease.

Band size affects bust size. Every DD is different. Cup volume increases as band size increases.

Cup Volume increases as bust letters increase within a single band size.

More on sister sizes, head over to you Fitting page!

Love A&Fx

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