The Real Gas Equation Calculator uses the van der Waals form of the real-gas equation, (P + a(n/V)^2)(V - n b) = n R T, to account for intermolecular attractions (a) and finite molecular size (b) that the ideal gas law neglects; enter any three of the four main variables (P in atm, V in L, n in mol, T in K) and the calculator will solve for the missing one — pressure and temperature are computed directly while volume or amount are found numerically using a Newton–Raphson solver because the equation is nonlinear; be sure to supply sensible van der Waals constants and initial guesses, and note that solutions are only physical when V > n·b and when the numerical solver converges.