I absolutely love this waist trainer! I'm 5'8" and 154 pounds and I got a small, it fit well but I definitely could have gotten an xs, so it does run a bit large,  but in retrospect I've been waist training for a few years now so if this is new to you, a size smaller should work just fine !:) this waist trainer is CRAAAAAZYYYY COMFORTABLE! !! I had a waist trainer from a different brand before this, that was very uncomfortable and left bruises, but this waist trainer is so comfortable and breathable I've fallen asleep with it on! Great buy for anyone, for beginners or people who don't wait train on a daily bases I would recommend getting a size smaller but if you waist train daily I would recommend getting two sizes smaller than your usual. But I will definitely be buying from this company again!