I'm 5'7, 160 pounds, and a 34c bra size. I usually wear a size small in shirts and a size 8 in pants. I usually also buy bathing suits in a size small but this one I got in a size large. It fits just right, any other smaller size would not have fit due to my long torso. The back part is full underwear not a thong. The straps are not adjustable.