If you don't have a Nordstrom near you, their website has great videos explaining how to measure for your size. I've yo-yo'd weight in the last few years and I'd say in the last 4 years I've worn a 34A, 36A, and now 34B. I had no idea I went down in band size after doing a half a year of boot camp classes and it was such a huge relief to have the band stay down in the back! I also second the Victoria Secret odd sizing comment above. While friendly they only seem to carry limited "average" sizes. If you're anything A cup they don't carry it in store and will measure you as a B. My BFF who is a DD got measured as a D with a waaay too big band so that they wouldn't have to turn her sale away. Cute styles and prints, if you fit the limited inventory.