I usually wear a medium in women's tops and a large in juniors tops. I went for a medium because I figured tank tops should be a little form fitting but the mediums are much too small. For reference, I am a 34ddd bust and have a thicker hourglass figure. It squeezes my hips and boobs and fits snug around my waist. I'd go for a size up or at least expect very snug fitting tops.

The quality of the tanktop is good--I will repurchase (a size large this time) when the mediums wear out.