I am usually a S in rompers and based on the reviews it does run a tad bit big based on the design of the romper so I recommend sizing down because the area by the legs are big and stomuch. There is a waist band which you can tighten but it does not do much as the waist band is elastic. I wish I would have gotten an XS but it is a final sale item so I cannot return it. It's cute buy it!

Item fits nicely