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# Reduced pressure

In thermodynamics, the reduced pressure of a fluid is defined as its actual pressure divided by its critical pressure.

$P_r = {P \over P_c}$

These dimensionless themodynamic coordinates (together with the reduced temperature) provide the basis for the simplest form of the theorem of corresponding states.

The reduced pressure is often used in thermodynamical formulas, e.g. the Peng-Robinson equation of state.