The specific gas constant of a gas or a mixture of gases (R) is given by the molar gas constant divided by the molar mass (M) of the gas or mixture:
Just as the molar gas constant can be related to the Boltzmann constant, so can the specific gas constant by dividing the Boltzmann constant by the molecular mass of the gas:
Another important relationship comes from thermodynamics. Mayer's relation relates the specific gas constant to the specific heat capacities for a calorically perfect gas and a thermally perfect gas:
where c is the specific heat capacity for a constant pressure and c is the specific heat capacity for a constant volume.
It is common, especially in engineering applications, to represent the specific gas constant by the symbol R. In such cases, the universal gas constant is usually given a different symbol such as  to distinguish it. In any case, the context and/or unit of the gas constant should make it clear as to whether the universal or specific gas constant is being referred to.
In case of air, using the perfect gas law and the standard sea-level conditions (SSL) (air density ρ = 1.225 kg/m, temperature T = 288.15 K and pressure p = ), we have that R = P/(ρT) = . Then the molar mass of air is computed by M = R/R = .