I am 5' 6", 125-130, and I ordered the Medium. It fit perfectly, by which I mean it skims my body (which is the correct fit for a 1920s dress). It doesn't fit tight like the promo images. I bought it for a 1920s event.

It's a beautiful dress, very heavy from all the beads/sequins, feels much more expensive than the price I paid. I couldn't see any flaws in the beadwork. It's perfect for a fancy 1920s event.

I'm actually returning it, because I decided to go in a different direction with my outfit. But the quality and fit are superb, would highly recommend.