This was purchased because I forgot my workout wear. It has a built-in bra, so you can wear it as a single layer. I had it altered because the size was too big, but I've only worn it twice. In my personal opinion, it's a size S, but I think it could fit someone who usually wears a size M. I will remove the altered parts before listing it. The alteration marks are slightly visible, but they are not visible from the outside.