To help you find the right size: underbust:31" and over:35". = Size 2.
I had trouble deciphering their specific size chart, so consulted customer service. They recommended size 3. Wrong. It was too big. I returned for size 2. Band fits right now. Size 2 can definitely accommodate bigger bust, wouldn't be great for smaller. Had to shorten shoulder straps all the way also. (5'2"). Comfy though and love the color.