In the formula P*V = n*R*T, which is a relation between the volume V occupied by n moles of a gas at a temperature T and a pressuer P, R is a physical constant referred to as the gas constant, ideal gas constant or universal gas constant.
If P, V and T are expressed in terms of SI units, the value of the gas constant is 8.314 J/(K*mole). It has a different magnitude when P, V and T are expressed in other units.
R is called as the gas constant. The value of the constant depend upon the unit of the variable present in the equation.
If Pressure is measured at "atm", volume in "liter", temperature in kelvin a. then the value of R is 0.0820 L atm/(mol K)