Osmolarity and osmolality both measure the concentration of solute particles in a solution, but osmolarity is based on volume while osmolality is based on mass. Osmolality is preferred in physiological conditions because volume can change with temperature whereas mass remains stable.

1. Osmolarity
vs.
Osmolality

2. Solute
Solvent

3. Osmolarity
Solute in
osmoles
Volume of the
solventliter

4. Osmolality
Solute in
osmoles
Weight of the
solventkg

5. Volume changes
with heat
But mass
does not

6. Although temperature is
fairly stable in
physiological
conditions…

7. More preferred term is
Osmolality