The ideal gas law, also called the general gas equation, is the equation of state of a hypothetical ideal gas. It is a good approximation of the behavior of many gases under many conditions, although it has several limitations. It was first stated by Benoît Paul Émile Clapeyron in 1834 as a combination of the empirical Boyles law, Charless law, Avogadros law, and Gay-Lussacs law. The ideal gas law is often written in an empirical form:
where ,  and  are the pressure, volume and temperature respectively;  is the amount of substance; and  is the ideal gas constant.
It can also be derived from the microscopic kinetic theory, as was achieved (apparently independently) by August Krönig in 1856 and Rudolf Clausius in 1857.