The **Ideal Gas Law** is a combination of Boyle's Law, Charles' Law and Avogadro's Law. It can be expressed by a single equation, **PV = nRT**, where P is pressure, V is volume, n is the number of moles, R is the general gas constant, and T is the absolute temperature.

The value of the gas constant, R is 8.3143 J K^{-1} mol^{-1}. Note that these are SI units, and therefore the volume used in this equation must be in m^{3}and the pressure in N^{-2}. In all gas law calculations, absolute values of temperature (Kelvin) must be used.

Another commonly encountered value for R is 0.08205 atm dm^{3} K^{-1} mol^{-1}. If this value is used then the volume must be in dm^{3} and the pressure in atm.

See also Boyle's Law | Charles' Law | Ideal Gas | Avogadro's Law.