Boyle's law-named for Robert Boyle-states that, at constant temperature, the pressure P of a gas varies inversely with its volume V, or PV = k, where k is a constant.
Charles's law-named for J.-A.-C. Charles (1746–1823)-states that, at constant pressure, the volume V of a gas is directly proportional to its absolute (Kelvin) temperature T, or V/T = k.
These two laws can be combined to form a single generalization of the behaviour of gases known as an equation of state,
PV = nRT,
where n is the number of gram-moles of a gas and R is called the universal gas constant. Though this law describes the behaviour of an ideal gas, it closely approximates the behaviour of real gases.