# Charles' law

Charles' law states that for a gas held at constant pressure,
the volume (*V*) occupied by the gas
is directly proportional to its temperature (*T*). That is:

*V* ∝ *T*, or

*V*/*T* = *k*,

where *k* is a constant.

The relationship was discovered by Jacques Charles in 1787 and is a special case of the ideal
gas law. It is sometimes called **Gay-Lussac's law**, because
Joseph Gay-Lussac established it more
accurately in 1882.