I got the onesie for a pajama party and it's my first time ever wearing one. I'm 5'3 and normally wear a 2X so I got a 3x just to be safe. It fit just as expected however it was a little long on me. If you want to be comfortable go a size up if not stick to your regular size. The only down side is the half zipper so it does make it a little hard to take it off