I have big boobs. Like, massive, back pain, can't wear certain tops, I'm definitely having a boob job some day big. It's incredibly uncomfortable, and I've struggled with finding proper bras for years. While I was out shopping on Sunday, I decided to check the bra section for the one size I knew I fit. After a tiny stress-panic when I didn't find it, because of course I didn't, I remembered reading an article about sister sizes, and immediately did a quick google search. There are a ton of helpful guides and charts to find your own sister size, and you can find the one I used here. My own, for instance, is a 34DD/E. The bras I purchased were 38D.
At this point in time, I've only worn one of the bras once, but it fit just fine, and the two are identical. I knew the trick was supposed to work, but I had my doubts. However, I was pleasantly surprised. It's helpful, and I just wanted to pass the tip along.
PS: Apologies for the extra noisy photos. Storm season is upon us over here.