For an ideal gas, which is one where the molecules of the gas are considered to have a negligible size, move randomly and there is no interaction between the gas molecules or within the gas molecules, the ideal gas law provides a relation between the volume, temperature, and pressure of the gas.

This is given by P*V = n*R*T, where P is the pressure of the gas, V is the volume of the gas, n is the number of moles of the gas, R is a constant known as the gas constant and T is the temperature in Kelvin.

Ideal gases do not change state irrespective of the temperature and pressure applied. Under normal conditions that most experiments are conducted at, the ideal gas law gives results that are a very close approximation to the actual behavior of gases.