We need to know the molar concentration of dissolved species in order to calculate the osmotic pressure of an aqueous solution. We calculate the osmotic pressure, (pi), using the following equation:
M is the molar concentration of dissolved species (units of mol/L).
R is the ideal gas constant (0.08206 L atm mol-1 K-1, or other values depending on the pressure units).
T is the temperature on the Kelvin scale.