When Amagats law is valid and' the gas mixture is made of ideal gases,
where:
:  is the pressure of the gas mixture,
:  is the volume of the i-th component of the gas mixture,
:  is the total volume of the gas mixture,
:  is the amount of substance of i-th component of the gas mixture (in mol),
:  is the total amount of substance of gas mixture (in mol),
:  is the ideal, or universal, gas constant, equal to the product of the Boltzmann constant and the Avogadro constant,
:  is the absolute temperature of the gas mixture (in K),
:  is the mole fraction of the i-th component of the gas mixture.
It follows that the mole fraction and volume fraction are the same. This is true also for other equation of state.