The answer is no. The idea that all cups of the same letter are the same size is a myth.
Pretend you’re a 34D. The “34” number is your band size. This number relates to your underbust measurement. The wider your ribcage is, the larger your band size will be. The “D” letter is your cup size. The cup size is the difference between your bust measurement and your underbust measurement.
This is where most of us get it wrong: 32D, 34D, 36D, 38D, and so on, do not have the same volume just because they are all D cups. The cup size alone does not indicate volume as you need to take into account the band size. Your cup size is relative to your band size.
As the band size gets bigger, the volume increases. That means that a person wearing a 32D has smaller breasts than someone wearing a 38D, despite them both wearing a D cup bra. In fact, a 38D bra is about three cup sizes larger than a 32D bra.
No bra size exists without both the band size AND the cup size – you can’t discuss one without the other. Yet many of us wrongly perceive that a D cup or larger as “big” sizes when discussing cup size in isolation.
Now you know that cup sizes are virtually meaningless without the band size, don’t get too attached to your cup size. Our bra size changes on average six times in our life! After a proper fitting, some women can be shocked to learn that they are a smaller or bigger size than they were before.
Ultimately, understanding and accepting your real size (both the band and the cup) will only help to have properly fitted bras that will make you feel more comfortable and supported.