31/03/2017 11:20 SAST | Updated 31/03/2017 16:00 SAST

Bra Sizing: Ever Wondered Why AA Cups Are Smaller But DD Are Bigger?

Lots of us are probably wearing one every single day, but that doesn’t mean we have the first idea about what is actually going on underneath our clothing.

Whether you’re rocking a strapless, balconette, full cup, half cup, or one of those suction devices that makes you feel like a cling-filmed bird, you’re going to need to make sure your bra is fitting correctly. 

Especially as, according to fit expert Monica Harrington at Triumph, 76% of women are still wearing the wrong size.


Sam Edwards via Getty Images

How do bra sizes work?

Bra sizing is broken down into two components – the band size and cup size – and the combination of both parts make up the figure that you look for on the hanger in the shop.

What is a band size?

The number at the front is your band size. This is the size of your rib cage, measured numerically, for example 30, 32, 34.

What is a cup size?

The letter is your cup size, and refers to the size of the breasts in relation to the rib cage, for example A, B, C, D.

What does cup size mean?

It is important to note that the cup size doesn’t represent volume, but instead represents how much bigger your breasts are than your rib cage.

In fact, the letter without the number is useless, as it is calculated directly in proportion to the size of your rib cage. For example, D cup breasts on a 28 band are smaller in volume than D cup breasts on a 40 band.

Why are AA cups smaller and DD cups larger?

There is no definitive answer as to why an AA cup is smaller than an A but the double-lettered cups that follow D (for example, DD, EE, FF) are all larger than their original size - it is made particularly confusing as there are no international standards for bra sizing.

But there are some theories.

The concept of cup sizing was first introduced in 1937 in the USA and later in the UK in 1948. 

This first incarnation had four sizes (A, B, C, D), which might be where the concept of D being a huge ‘glamour-model’ size breast could have first come from – aside from the fact Katie Price claimed to be a DD at the height of her career – when in reality 57% of women in the UK are actually a D cup. In fact the most common bra size in the UK is a 36D.

Then, when brands decided that these four sizes were not sufficient to cover the wide range of sizing, they added additional letters as markers of differentiation.

And rather than choosing an A- for example, they settled on an AA as a smaller alternative, and instead of jumping straight from D to E, they settled on a DD.

There is a difference of between 2cm and 2.54cm (depending on where you shop) between each cup size, so an AA is an inch smaller than A and DD is an inch bigger than D.