The Bra Fitter Diaries: My Sister Size, My Friend

Through some classic blogger over-sharing, you’re all aware by now that my bra size is 32E. But that’s not the whole truth. I’ve been holding out on you, and it’s time to come clean. *Deep breath* Friends, family, bra enthusiasts: I also wear a 34DD. Now, if you think we can recover from this small breach of trust, I’d like to tell you why I wear two different sizes.

It all comes down to sister sizes. These are bra sizes that share the same cup volume, like a 34DD and a 32E do. Remember last week, when I was saying that a cup size is meaningless without a band size? Here’s a perfect example of why that’s true. The following sizes all have the same cup volume: 40C, 38D, 36DD, 34E, 32F, 30FF, 28G.

Why do you need to know all this? Well, it comes in handy more often than you’d think. For example, some brands run small in the band, and some run big. So if you’re trying on a bra like that, it’s useful to be able to figure out a sister size. Here’s the rule to remember: if the number goes up, the letter goes down, and vice versa. Like so:

Ewa Michalak’s Cappuccino plunge bra is gorgeous and runs fairly true to size, so the 32E is great on me.

Cappuccino, by Ewa Michalak

I love, love, love my Lucy bra by Cleo. Since Lucy’s band runs a little snug, I find the 32E too small in the back. So I go up in the band to a 34, which means (according to our sister size rule) I need to go down in the cup to a DD. And voila, the 34DD is a perfect fit!

Lucy, by Cleo

In a bra that runs big, I’d make the same adjustments, but in the opposite direction. From a 32E, I would go down in the band to a 30 and up in the cup to an F. With the 30F, I’d get a snugger band than the 32E while keeping the same cup volume.

(A word of caution: The shape and structure of the cups – and, really, the whole bra – sometimes change when the cup size changes. For example, a 38E and a 30GG have the same cup volume, but can have very different shapes. The cups may become deeper, straps may widen, back may widen, etc.)

Sister sizes are one of the reasons that I rarely give a straight answer when a client asks me what her size is. Instead, I might say, “In this bra, your best fit is a 36G.” Because in a different brand or silhouette, a 34GG or a 38FF might actually be the best fit. So don’t be surprised if your bra wardrobe ends up including a couple of different sizes – that’s just the magic of sister sizes.