In chemistry, the constant R stands for the universal gas constant. R is equal to 8.31 joules per mole-Kelvin or 0.08 liter-atmospheres per mole-Kelvin. It is the expression of the Boltzmann constant, k, in units of energy.
R is most commonly used in the equation PV = nRT, which is the ideal gas law. The variable P is the pressure, V is the volume, n is the number of moles and T is the temperature. The universal gas constant is also used in the equation R = work/(amount x temperature). The exact value of R is based on the speed of sound in the gas argon.