I'm 5'4 and I ordered the XS. The straps are very long, so the front barely covers my chest. I have to sew the straps, which is annoying if you pay too much for a dress. If you are not tall, do NOT order this dress.
Really wanted to like these pants but the fabric was so thin/cheap it felt like they could have been $49 from Zara. The fit was cute (adequately high waisted) and I would wear them, but just couldn't justify it for the price.
I'm usually a 28 in jeans and I ordered a Large and they fit well.
I'm glad that I ended up sizing down, as the XS fits me perfectly. ( I am a size 4 or S in most clothes). I love that the buttons go all of the way down so I can button further down to make it work for the office and undo it a little to balance the long dress with some skin outside of work. I also love that this dress has some functional pockets on the seam, and putting a phone in the pocket doesn't mess up the lovely line of the garment either! A major sundress win! The fabric is also a great quality.