Why Your DD Cup Isn’t as Big as You Think

Let’s bust a myth right off the bat

We hear it all the time: “I’m a DD, that must be huge!” But what if we told you that a DD cup isn’t universally large? It’s true—your DD cup could be completely different from someone else’s DD, depending on one key factor: your band size.

Bra Sizes Are a Ratio, Not a Fixed Volume

Let’s break this down. A 10DD and a 16DD are not created equal. The cup volume of a 10DD is significantly smaller than that of a 16DD. That’s because bra cup sizes are always relative to the underband sizing.

Fun fact: A 12D actually has the same cup bust size as a 10DD. That’s called a sister size. Mind-blowing, right?

So, What Does DD Really Mean Then?

In simple terms, DD is just two cup sizes larger than a B cup in the same band size. So, if you’re wearing a size 12 band, your DD cups are based on that framework. This is how bra sister sizes and core cup sizes come into play.

The Misconception of ‘Big’

Thanks to media and pop culture, DD is often labelled as “massive.” But for many women, it’s a totally average size. In fact, the team at The Foundation sees DD and E cups walk through the door every day—they’re part of the core size and among the most common we fit.

What Matters More: Fit or Size?

Here’s the real tea: it’s not about how big the cup is. It’s about how well it fits. An ill-fitting DD can feel like a curse. A perfectly fitting DD? Heaven. That’s why using a comprehensive size guide is crucial.

Still Confused? Let’s Talk Sister Sizes

To help you out, we always recommend looking at our detailed size guide. If your DD cup feels off, you might be better suited to a D or E in a different band. It’s all about trying a few bra size options opening and using the correct sizing method.

Sister sizing is your friend here. A 12D = a 10DD = a 14C in cup volume. Confused? Our size chart breaks it all down.