Bra Guide: Not all D cups are the same size

I know that bras can be confusing little minxes. When I try to explain to someone that besides their 34G bra, they could also wear a 32GG, they look at me with bewilderment. This post aims to give you an easy-to-understand guide to how cup sizes work.

It’s a common misconception that all D cups hold exactly the same volume of boob, and then that cup size is just sewn onto different lengths of the band to make the 30D, 32D, 34D, etc., is not true.

Why All bra sizes are not created equal

In reality, cup size is determined by breast width, not breast volume; this means that two women with D cups can have very different-sized breasts. One may have a small frame and be considered petite, while the other may have a larger frame and be considered plus-size. The key to finding the right bra is to focus on fit, not cup size.

Read: Sports Bra Guides 14 Points to Avoid Buying Mistakes

Make sure the band is snug, and the cups encapsulate your entire breast without any spillage. If you’re unsure of your size, visit a lingerie store or get fitted by a professional bra fitter.

In my world of D-K bras* you may think there are only 11 cup sizes (D, E, F, FF, G, GG, H, HH, J, JJ, K) However, there are actually SIXTEEN different cup sizes, or more accurately, cup volumes (volume refers to the amount of breast tissue a cup can hold).

In this table below I have colour co-ordinated all the D-K BRA SIZES THAT HAVE CUPS WITH THE SAME VOLUME.

Bra Guide Not all D cups are the same size

As you shop for bras, you’ll notice six band sizes for each cup letter; bra sizing is not standardized, and different brands use different measurements. As a result, you may need to try on several bras to find the one that fits you best.

The band size is the number part of your bra size (for example, 32, 34, 36). The cup letter is the lettered part of your bra size (for example, A, B, C). Band sizes range from 28 to 40, and cup letters range from AA to DDD.

There is no real “average” bra size, as women come in all shapes and sizes. However, the most common bra size in the United States is a 34B.

 So, for example, a 28D has a #1 cup volume, a 30D has a #2 cup volume, 32D has a #3 cup volume, and so on.

Real Life Example

Imagine you wear a 36D; your cups fit well because they encase your breasts, but your band keeps riding up. Instead of thinking of your boobs as a D cup, you can think of them as being a cup volume #5. When you realize your band keeps riding up because you actually need a 32 band, not a 36, then you can see that a #5 cup volume on a 32 band is actually an F cup.

What is Sister Sizing?

When people talk about sister sizing, they’re referring to all the bras with the same cup volume but on different length bands. In our chart, all the bra sizes with the same cup volume number are sister sizes. For example, 28JJ, 30J, 32HH, 34H, 36GG, and 38G are all sister sizes to each other because they’re all cup volume #10.

I hope this has helped (I expect I’ve confused a few people too). If you have any questions, leave a comment below, and I’ll get back to you xx

*A footnote for anyone wondering why I don’t use UK DD cups; it’s because they are the same equivalent as US D cups, so to avoid confusion, I don’t use the DD size.