Understanding Sports Bra Sizes – What do they Mean?

16/12/2020

Sports bra sizing is one of the most important but also one of the most confusing aspects of buying a sports bra. The combination on numbers and letters represent our back and cup size. But how can I fit a 12DD, 34DDD and also a 75E? No wonder we women get our sizing wrong so often!

In this article I will break down the numbers and letters and explain why they vary so much across styles, brands and countries. Read on.

The Number

Your sports bra size starts with a number, in my case 12. This is your sports bras ‘band’ size and is found by measuring horizontally around your ribcage, directly under your breasts.

Interestingly this number has nothing to do with the actual measurement. But is rather a number derived from your measurement using a bra size calculator to determine your size. It relates in terminology to your dress size but is often not the same. You can wear a 12 dress and a 14 sports bra!

In Australia and New Zealand, they are only ever even numbers:

6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28

If you measure yourself and find you are between sizes it is recommended you go up to the next even size. If you would like more info on sports bra sizing please check out my article ‘Finding Your Bra Size at Home’.

The Letter

After the number there is a letter or letters, in my case DD. This is your sports bras ‘cup’ size and is found by measuring horizontally around the fullest part of your breasts.

Once again, this number is plugged into a bra size calculator to find your cup size. The determined letter refers to the size of your sports bras cup and measures the volume of breast tissue it holds. The higher the letter, the greater the volume. Australian cup sizes are as follows:

A, B, C, D, DD, E, F, FF, G, GG, H, HH, J, JJ, K

Traditionally your cup size was found by subtracting the difference between your two measurements. A one-inch difference was an ‘A’ cup, two-inches a ‘B’ cup, three-inches a ‘C’ cup and so on. In Australia we have since converted to the metric system, so this rule is no longer used but can be a good cross-check if you are used to the imperial system.

Considering this, not all cups are created equal. A 12D cup is not the same as an 18D cup as the volume of breast tissue needed to fill an 18D is much more than for a 12D. Sounds confusing but it is simple maths (Ok I agree, complex maths). A four-inch difference on a larger back size equates to a larger volume bust and thus a larger cup size to hold that volume. It is all about proportion. Make sense?

Why the double and sometimes triple letters you ask? For international cup sizes less than an ‘A’ cup. manufacturers needed letters that represented less than an inch and there are no letters below ‘A’. Thus, ‘AA’ and ‘AAA’ were born.

Historically women did not want to appear too big. As such, manufacturers discovered women were more likely to buy a ‘DD’ cup than an ‘E’ cup because ‘DD’ sounds smaller. In some countries ‘DDD’ cups were introduced to accommodate.

Combining the Two

 Phew, that is a lot to get through and to digest. Well done! Next, we combine the two to get the combination we are all used to seeing on our sports bras.

My ‘12’ back combines with my ‘DD’ cup to give me a sports bra size of 12DD. It is now simply a matter of going shopping, right? If only it was that easy…

International Sizing

To confuse things even more varying countries represent back and cup sizes differently. A 12DD in Australia is a 34DD in the UK, a 34DD/E in the USA and a 90E in France!

The UK and USA still measure using the imperial system and the ‘34’ is simply your chest measurement in inches (I measure 34 inches). France and Spain are metric, and their sizes relate as such. 34-inches = 86.5cm = 90 (remember to always round up!). And I won’t even mention Italy!

It is important to understand these size nuances when considering international brands. Luckily, I have made it all the easier for you with my bra size conversion guide.

Sister Sizing

Hopefully, you have a better understanding of sports bra sizes and how they work. This now leads us to sister sizing.

We know that the size of the band relates to your chest size and the volume of the cup relates to the band size. So, if you are having trouble finding a size that fits you can try ‘sister sizing’ up and down a band size.

Quite simply if the cup fits well but the band is too tight, go up a band size and down a cup size (remember cup volume?). If your band is too loose go down a band and up a cup.

10E – 12DD – 14D

Check out my sports bra sister size guide for more info.

My Final Thoughts

Wow, that was a lot to get through. Well done. Fingers crossed you now understand all about sports bra sizes (they aren’t that confusing, are they?)

Given your new understanding it is important to ensure you are wearing the correct size (up to 80% of women don’t!). Your sports bra needs to fit you to support you. If you are not sure my fitting room has a whole lot of info to help you find the perfect fit.

If you need any further help or advice, please do not hesitate to get in touch.

Your is support.

Amy x


Amy is the face behind Sports Bras Direct, Australia’s largest sports bra website. She's a mother of two, outdoors lover and sports bra expert. Her life mission is to help active women get the support they need as well as assisting women in need through her charitable donations.

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