In thermodynamics, the internal energy of a system is the energy contained within the system. It excludes the kinetic energy of motion of the system as a whole and the potential energy of the system as a whole due to external force fields. The internal energy of an ideal gas is proportional to its mass (number of moles) N and to its temperature T. Given here is an online internal energy of an ideal gas calculator to calculate the internal energy of the monatomic gas.