I ordered a medium because my chest measures 36'' but I am petite (size 30 bra) and the medium was too big around my torso. Customer service helped me decide on a SMALL vs XS as they said there is a fairly big difference between sizes. The Small fits perfect. The fabric stretches a lot and is super soft so I recommend sizing down if in question!
I went off the size chart (chest 36 inch, large boobs but petite frame) and ordered a medium but it is too big on the arm straps and I don't fill it out all the way. I am 110 lbs. The fabric is REALLY stretchy but so soft and great quality. I will reorder in smaller size, torn between S and XS though. Hope this helps! I got the White Illusion Leggings too and they are perfection, I wear XS and true to size and not too long!
I was worried it was going to be a cheap material but it isn’t. It’s almost like a real sports bra, only not as tight around the chest. Very comfortable and soft material. The black part around the bottom is a thick, strong elastic band. Very good quality. Definitely plan to purchase more items down the road. I wear a small in men’s T-shirts’ and usually a medium in women’s. I ordered a medium for the top.