Bra Sister Sizes: How Band and Cup Sizes Work

How Bra Band Size and Cup Size Work Together

The single most important thing to know about bra size is that when you go up a band side, you need to go down a cup size, to maintain the same cup volume. Most women don't know this. So they move from, say, a 34C to a 36C. I think they just went up a band size, when in actuality, they went up a band size, and cup size. I know this sounds confusing, so let me show you what I'm talking about.

Why Cup Volume Changes With Band Size

Here are four bras with the same cup size. Now, most women think all these bras should have the same cup volume, because they are all D cups. Well, as you can see, they are not. These D cups are getting bigger, and the band size is increased, because the base of the breast gets larger.

How to Keep the Same Cup Volume

Now, here is the exact same bra style, but this time, as we go up a band's size, we're going down a cup size. See how all these cup sizes look the same? Well, they are the same.

Why the Same Cup Letter Can Have Different Cup Volumes

So let's go back to this earlier exhibit. Why are these D cups not the same volume for all band sizes? The answer is in the measuring. A cup size is a representation of breast projection, or how far it projects from your body, not how much volume it contains. After all, you measure your body diameter to find your cup size, and every one inch increase is another cup size.

How Band Size Affects Bra Cup Volume

As the band gets bigger, the base of your breast, too, gets wider, and this increases the bottom in your cups. So, again, a cup letter represents the projection off your chest.

How to Change Band Size and Maintain Cup Volume

So now you know the cup size game. Want to go up a band and keep the same cup volume, then go up a band, go down a cup size. Conversely, want to go down a band, keep the sand cup volume, go down a band, then go up a cup size. And that's the cup size game.