MOSSO specifies the ring sizes by the inner circumference of the ring in millimetre (mm). For example size 44 corresponds to 44 mm.
How to determine your ring size
You can easily determine your own ring size with a measuring tape or a cord. To measure simply place the cord (or the measuring tape) around the finger where you want to put the ring. The ends of the cord should be marked.
Use a ruler to measure the cord and determine your ring size in mm.
Below chart shows how MOSSO sizes translates into other sizes: