Light snow accumulation means sub advisory for that forecast period i.e. around 1", 1-2, 1-3, 2-3
Moderate means advisory for that period
Heavy means warning for that period
Adding an inch to say 1-3 yields about 2-4ish. That's generally how that works in my experience. @OceanStWx can correct me if im wrong.
Light, moderate, heavy are the three categories and its usually stated outside of a time when exact numbers come into play.