the osmolarity of a simple solution is equal to the molarity times the number of particles per molecule. For substances that maintain their molecular structure when they dissolve (e.g. glucose), the osmolarity and the molarity are essentially the same. For substances that dissociate when they dissolve, the osmolarity is the number of free particles times the molarity. Thus for a pure NaCl solution, a 1 Molar solution would be 2 Osmolar (1 for Na, and 1 for Cl).
glucose has one particle/molecule
NaCl has 2
CaCl2 has 3
50mM glucose x 1 = 50m osmoles
50mM NaCl x 2 = 100 m osmoles
50 mM CaCl2 x 3 = 150 m osmoles