High Quality Content by WIKIPEDIA articles! The combined gas law is a gas law which combines Charles`s law, Boyle`s law, and Gay-Lussac`s law. These laws each relate one thermodynamic variable to another mathematically while holding everything else constant. Charles`s law states that volume and temperature are directly proportional to each other as long as pressure is held constant. Boyle`s law asserts that pressure and volume are inversely proportional to each other at fixed temperature. Finally, Gay-Lussac`s law introduces a direct proportionality between temperature and pressure as long as it is at a constant volume. The inter-dependence of these variables is shown in the combined gas law, which clearly states that: