I usually wear a XS, i got an S and it fits amazingly! If you like larger pants got up 2 sizes
I'm really short and have a small waist so it's hard to find nice fitting sweatpants but these are perfect. The adjustable waist is great and the length isn't too long. These are my best fitting sweatpants! For size reference, I'm 5'0 and have a 23" waist.