# PlanetPhysics/Ideal Gas Law

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The equation that characterizes any amount of a gas is

where is the pressure, the volume, the number of the gas moles and the absolute temperature of the gas; the universal gas constant (approximately 8.314472 ).

The gas law is accurately valid for an ideal gas, but a good approximation for real gases.

The law contains the following gas laws:

- Boyle--Mariotte law (\, constant when and are constants)
- Gay--Lussac law (\, constant when and are constants)
- Avogadro's law (in equal conditions, equal volumes of different gases contain the same number of molecules)

### Alternative definition edit

The ideal gas law can also be defined using Boltzmann's constant:

The symbols are those defined above, with the difference that is the number of gas molecules, and is the Boltzmann constant, . This form is often preferred by physicists who consider the number of molecules to be more fundamental than the number of moles.