Cup Size Explained

There are two components of a bra size: the number, and the letter.

The numerical component corresponds to your ribcage measurement, going up or down depending on your preference for a relaxed or firm band. But what exactly does the cup size mean?

Contrary to what many people believe, your cup size is not a measurement of breast volume. Your cup size represents the difference between your bust measurement and your band size.

There are two components of a bra size: the number, and the letter.

The numerical component corresponds to your ribcage measurement, going up or down depending on your preference for a relaxed or firm band. But what exactly does the cup size mean?

Contrary to what many people believe, your cup size is not a measurement of breast volume. Your cup size represents the difference between your bust measurement and your band size.

Your cup size equals bust measurement minus band size

If your bust is 1’’ bigger than your band size, your cup size is A. If your bust is 2’’ bigger than your band size, your cup size is B. If your bust is 3’’ bigger than your band size, your cup size is C. For each additional inch, you go up a cup size.

Cup size: International Systems

In most of North America, cup sizes go from A to D, then DD, then DDD, then back to the alphabet (G, H, I…). In the U.K., cup size letters start doubling at D, skipping E, then start doubling again at F. In most of continental Europe, cup sizes go down the English alphabet.

Cup size: International Systems
Breasts are irregular 3D objects, not perfect spheres - the same goes for bras

What does this mean?

It doesn’t make sense to say “I’ve never been a DD, that’s huge!”

Cup sizes are not static. They translate to different volumes when combined with different band sizes. For example, 30DD has the same cup volume as 32D, 34C, and 36B. These four sizes are “sister sizes.” They share the same breast volume, which is roughly 480 cc. Someone who is a 30DD actually has smaller breasts than someone who is a 36A!

It’s normal to have bras of a few different sizes.

Breasts are irregular 3D objects, not perfect spheres – the same goes for bras. In a perfect (but slightly creepy) world, we can take our breasts off and measure their volume and shape, then match them to the perfect bra. The system we’ve got, which takes underband and bust measurements and spits out a bra size, is an approximation.

Depending on the shape of the bra, sometimes a neighbouring size will fit you better than your go-to size. (For example, if you are shallow on top, and full on bottom, you’ll likely need to cup size down when wearing a bra with a tall and voluminous upper cup.)


As always, how the bra feels on you is your best guide. Bra sizing can be complicated – trial and error is the most reliable way to find something that works for you. Never settle for discomfort.

As always, how the bra feels on you is your best guide. Bra sizing can be complicated – trial and error is the most reliable way to find something that works for you. Never settle for discomfort.


Why We Made Salma
Band Size Explained
Cup Size Explained