The ideal gas law is the equation of state of a hypothetical ideal gas. It is a good approximation to the behavior of many gases under many conditions, although it has several limitations. It was first stated by Émile Clapeyron in 1834 as a combination of Boyle's law, Charles's law and Avogadro's Law. The ideal gas law is often written as:

where the letters denote pressure, volume, amount (in moles), ideal gas constant, and temperature of the gas, respectively.