The description says size 3-4. Runs big more like 5/6.  My son is a 3T and it has these "boot covers" which he keeps tripping over.. Lots of room in the suit as well. Mask doesn't fit  right.  Hard for him to see which frustrates him.
Might for next year or thinking about cutting the boot covers off and making better breathing holes. At least it wasn't too expensive and extra padding for the " muscles" are cute.