Here's Zipia's size chart
Zipia doesn't size an XS but going by these measurements I would probably say it fits in the MEDIUM category. Zipia is not the brand, they are the online distributor. The brands are various Korean brands like ROTTA, Overflow and DUDE.
Sometimes you get lucky with Zipia... I got a knockoff of a Rick Owens DRKSHDW jacket from another forum member. It was sold as an Overflow piece but the tag said something different (don't recall the exact name) - I googled the name and found out that my knockoff jacket came from the same manufacturer that made the real Rick Owens jacket!