An ideal gas is an idealized model for real gases. Real gases behave according to this model if their densities are sufficiently low. The condition of low density means that the molecules of the gas are so far apart that they do not interact.

The pressure of an ideal gas depends on many factors. The pressure increases as the temperature (Kelvin temperature) increases. It also increases as the number of molecules or the number of moles of the gas increases. It is also possible to increase the pressure of a gas by reducing its volume. If the number of molecules and the temperature are kept constant, the pressure of an ideal gas decreases as its volume decreases.

If these three relations are put together in an equation by inserting a proportionality constant , called the universal gas constant , it can be written as :