I bought a XS-M and my waist is 29"in. The minimum waist size for XS-M is 25"in. If you decide to opt for the next size up, the Waspie will be looser and not cinch in your waist tightly, so keep that in mind if that is something you want from this Waspie. Otherwise, it's a great piece for making outfits look extra stylish. There is a light stretch to the fabric and the structure is not stiff, so there is room for movement.
I love this. It's incredibly romantic. Fits just as I had hoped to.