Why does the gas constant have the same value for every ideal gas?

The universal gas constant (R) has the same value for every ideal gas because it is a fundamental physical constant defined as the product of Avogadro’s number (Nₐ) and the Boltzmann constant (k).12

Because the ideal gas law (PV = nRT) is derived from the kinetic theory of gases, it assumes that all gases consist of a large number of molecules in random motion where individual molecular volume and intermolecular forces are negligible. By using the mole—a unit based on the number of molecules—as the standard for measuring the quantity of gas, the constant R accounts for the energy per degree per mole. Consequently, when comparing one mole of any gas under ideal conditions, the relationship between pressure, volume, and absolute temperature remains consistent across all substances.321