Osmotic pressure of a dilute solution is expressed by van't Hoff's equation as:

For a dilute solution behaving ideally, $\pi = C R T$, where $C$ is the molar concentration of solute, $R$ the gas constant and $T$ the absolute temperature. Equivalently $\pi V = n R T$, structurally identical to the ideal-gas equation with osmotic pressure playing the role of $p$.