Honestly, VS is the worst for fittings. I used to work at Lane Bryant and we did fittings too. We once had a customer come in right after she had a fitting at VS. They told her she was a 34B. There was no way this girl was a B cup. She was bigger than me and at the time, I'm a DD.
Lady Grace is another option for a good fitting, if you have one anywhere near you. Or even Lane Bryant if that's the only place you can go. They say they're "certified" at LB, but to be honest, the certification that I got was to watch a video and read a pamphlet. And suddenly I was a certified bra fitter.
You can actually measure yourself, but I've actually seen it done a couple different ways, so I think it actually depends on where you buy too.
To measure: first take the tape measure and put it around under the girls. This is your band size. Now if you measure in at 35 inches, you'll need a 36 because bras only come in even sizes.
Next, measure across the girls at the fullest part. Find the difference between that number and the band size to determine the cup size.
1 inch = A
2 inches = B
3 inches = C
4 inches = D
5 inches = DD
and so on.
Hope this helps!
And once you're in the right size, you'll be a new woman. You'll notice your clothes fit better and you walk straighter. It's amazing. I remembe a customer who came in after losing a good deal of weight and she wanted a fitting. She was adamant that she didn't want underwire because they hurt. We got her to try on a couple anyway, after we measured her, and when she left the store, she had bought 4 underwire bras and was wearing one of them. She tossed her old bra in the trash before she even left. The right bra makes a world of difference. And honestly, spending the extra $$ is so worth it.