In this Demonstration, you can solve for any of the four variables in the ideal gas law, , given the other three. In SI units the pressure is expressed in pascals (Pa), equal to . Since one standard atmosphere equals 101.325 kPa, the SI pressure units are given in kPa. Volume is in , temperature in K, and number of moles in mol. The universal gas constant J/K mol (it is divided by 1000 so comes out in kPa).

In the older, but still extensively used liter-atmosphere system of units, is given in atm and in L, and the gas constant is L atm/K mol. The temperature on the Celsius scale (°C) is also shown.

At low temperatures or high pressures, the ideal gas law becomes inaccurate and you must use another equation of state, such as the van der Waals equation.