Now, these measurements aren't always correct, and that's why I urge women to go to someone who is trained in how to do bra fittings. If you'd rather do it at home, this WikiHow page and this HerRoom page do a great job of detailing the measuring process.
The bulk of your bra's support should come from the BAND AROUND YOUR CHEST. Now, as someone with asymmetry, I'm thinking, "no it shouldn't, it's the straps," but that's not the case. You see, if your bra doesn't fit right around your ribs, then you run the risk of your bra sliding down constantly. We can't have this. This SHOWS asymmetry way more than you could ever imagine. So, you have to get the right BAND size. Now, when it comes to the cups, you have to fit to your larger breast. HOWEVER, there's a catch to this. I am a 34DD, but many of the 34DD bras don't work so well for me. My implant/weirdo boob/asymmetric breast might sit nicely in a 34DD, but my natural breast is spilling out like a glass of pop that was poured too fast! This is about the time where the panic starts to set in. You start having that meltdown and your eyes well up with tears. Calm down, I say! There's a secret! Bras have "sister sizes," which is probably the best gift to asymmetry the industry could have given. So, let's say your larger breast doesn't like a 34DD, and you're getting some weird muffin-boob thing going on. Try on a 36D instead! Now, you might be saying, "I didn't measure a 36, Danielle. I measured a 34, and I'm not a D, I'm a DD. I got measured like you told me to!" Trust me. If you go UP one band size, but go DOWN one cup size, it's almost like the same bra! You can go DOWN one band size and UP one cup size if you feel like the cup is too small for your breasts, too. So, you try on a 36D and you find that you have minimized muffin-boob/spillage for your larger breast, and your smaller breast will actually look different in the cup, too. This provides just a little more room for your smaller breast, but allows your larger breast to fit more naturally into the cup.
Let's get to the straps now, shall we?
THERE IS ONE IMPORTANT NOTE I MUST MENTION! YOUR BRA MUST MUST MUST HAVE FULLY-ADJUSTABLE STRAPS. This means that your bra cannot have some fancy design on the front of the straps and only allow you 4" of adjustment room in the back. This will not work and will in no way help your asymmetry. You cannot use a bra that does not have fully-adjustable straps. Fully-adjustable means that you could take the adjuster piece all the way to the front of the bra if you wanted to. Again, your bra MUST HAVE FULLY-ADJUSTABLE STRAPS.
Now that you've been fitted with the CORRECT SIZE bra, we can talk about how to adjust your straps. When we were picking the bra out, we catered to the LARGER breast, now we cater to the smaller breast in some ways. So, if you have some pretty drastic asymmetry, this part will be pretty difficult. For DRASTIC asymmetry (2 or more cup sizes), I'll address everything at the end of this post. Drastic asymmetry has to be handled a little differently. Don't worry, ladies, I'll handles those breasts, too! No breasts are left out in my blog!
Adjusting the shoulder straps on a bra is one of the most important parts of hiding breast asymmetry. Women seem to have this really weird notion that your straps absolutely must be adjusted to the same place on each side. Who came up with that idea? Why is symmetry so important in bra straps? Your breasts aren't symmetric, so why do you think your straps need to be? If you want to hide your asymmetry, you need to THROW THAT IDEA OUT THE WINDOW. Do it. Right now. Throw it out. Ok, now that it's gone, we can start fresh. Everyone wants perky breasts. Nobody has ever seen National Geographic-like boobs and said, "I want those!" It's just never happened.
My Biggest Pet Peeve: STOP BUYING GREAT BRAS AND IMPROPERLY ADJUSTING THEM. YOUR BREASTS SHOULDN'T SAG IN A GOOD QUALITY $50 BRA! THERE IS NOTHING FLATTERING ABOUT BREASTS THAT DRAG THE FLOOR OR COVER YOUR BELLY BUTTON.
Back when physics was discovered, mankind used physics to make the simple tasks of living far more enhanced. The wheel was invented, levers and pulleys were utilized, gravity was fought with might and valor, and buildings that reached the heavens were erected and supported. Somewhere along the way a bra was invented. The first bra was weird, and really didn't serve any real purpose for support.