For a sufficiently dilute gas (low density), both experiment and kinetic theory give the same relation among the three macroscopic variables: pressure times volume equals the mole number times the gas constant $R = 8.314\ \mathrm{J\,mol^{-1}K^{-1}}$ times the absolute temperature. This is the equation of state — every individual gas law (Boyle, Gay-Lussac, Charles) is a special case of it.