An ideal gas satisfies these conditions:
The ideal gas law states that:
PV = nRT
where P is pressure, V is volume, n is the number of moles, T is the absolute temperature, and R = 8.31 J/(mol K) is the universal gas constant.
This can be written in terms of N, the number of molecules, instead.
N = nNA, so:
PV = nNA (R/NA) T = NkT
where k is the Boltzmann constant, 1.38 x 10-23 J/K. This is the universal gas constant divided by Avogadro's number.