We present a molecular simulation method that yields simultaneously the equilibrium pitch wave number q and the twist elastic constant K-2 of a chiral nematic liquid crystal by sampling the torque density. A simulation of an untwisted system in periodic boundary conditions gives the product K(2)q; a further simulation with a uniform twist applied provides enough information to separately determine the two factors. We test our new method for a model potential, comparing the results with K(2)q from a thermodynamic integration route, and with K-2 from an order fluctuation analysis. We also present a thermodynamic perturbation theory analysis valid in the limit of weak chirality.