All garments are unisex sizing unless otherwise states. "Unisex" means slightly larger than women's sizing, and slightly smaller than men's sizing.
Ladies, for a snug fit, size down. For a loose fit, order your regular shirt size. If you are in between shirt sizes, size up! And if you want it oversized, go up a size or 2, but keep in mind, they typically get wider and not a whole lot longer.
I am 5'8, 185 lbs and a medium is fitted on me. A large is loose. And I wear XL for the oversized look.