The Biggest Misconception with Bra Sizing

This week I was casually reading an article from a popular women's lifestyle magazine and vented my frustration about a certain statement on my Instagram page. It's a very common and misleading statement so it's no wonder so many of us have misconceptions about bra sizes and how to find the right one.

The statement read; "A breast can weight more than a kilo when you are a D cup or above". So why is this wrong?

Understanding Bra Sizes

The letter of your bra size does not, I repeat, does not refer to a specific volume or size of breast. For example, the 'F' of a '34F' refers to the difference between your back (or underband) measurement and your chest measurement.

bra sizing measurement locations

You couldn't hold a boob in your hand and say "oh, this is probably a D cup" as a D cup is a different size on different back sizes. It's not a consistent volume and so we first need to find our right underband size before moving onto the next step and working out your cup size based on this.

Therefore, the earlier in the alphabet that your letter is, the smaller the difference is between these two measurements of yours. So, to put it another way, the letter refers to a ratio.

It can be a little hard to get your head around initially, so here's a diagram to help.

MAAREE bra grading, same cup

Above is an example of putting the same size/volume of breasts on people of varying back sizes. They have the same size and volume of boobs but the letters are different because their underband sizes are different.

Additionally, below is an example of bra sizes ending in the same letter across different back sizes. As you can see, the breast sizes actually get larger with back size, as the ratio between the two measurement is the same.

MAAREE bra grading, same letter

So if you've ever wondered why...

  1. Your petite friend has surprisingly large letters in her bra size,
  2. You can't find stick-on or backlass bras, that claim to be for specific cup sizes, to fit you,
  3. You've recently lost weight, but are surprised to find you need a bigger cup letter
  4. Changed your underband size but but surprised that the cup now doesn't fit, even though it's the same letter;

This. 👏 Is. 👏 Why. 👏

So, in theory, referring back to the initial incorrect statement, all cup sizes could actually weigh over and under a kilo.

Why don't we all know this already?

I fit women for my sports bras on a regular basis and I've come to realise that this isn't common knowledge and many never think to stray from the cup letter that they have worn previously. Even if they change their underband size.

Women wear bras on a daily basis, yet we aren't taught about bra sizes in school. If our mums also don't fully understand it then it's no wonder that so few of us are aware of this and still struggle to find our perfect size.

It can be a little tricky to fully grasp at first, so please take the time to thoroughly understand the diagrams above and please feel free to reach out if you need any more assistance or clarification. I'd be happy to help. But you nail it, you'll be a bra shopping wizard!

The most common scenario you may find yourself when trying on bras, is that you might need to go down an underband size, but want to keep the cup size. In this case you need to go down an underband size AND up letter, to keep the same volume of cup. The mantra I like to use is; 'if you go down in one, you go up in the other'. And vise versa.

"This is the sports bra of the future!"

- Claire Sanderson, Editor of Women's Health