An equation of state (EOS) for hard n-alkane models is proposed. This equation requires a previous knowledge of the second virial coefficient of the hard n-alkane model. Since the numerical determination of the second virial coefficient of chain molecules is computationally expensive, a new method for estimating the second virial coefficient of hard polymer models is proposed. This method yields predictions for the second virial coefficients in very good agreement with those determined numerically. In order to test the proposed equation of state, molecular dynamics simulations for repulsive n-alkane chains were performed. Excellent agreement was found between theoretical and simulated pressures for n-alkanes with up to 100 monomer units. The effect of changes in the torsional potential, bond angle, and bond length, on the equation of state of hard n-alkane models is analyzed. The equation of state is also extended to mixtures of hard n-alkane models. The proposed methodology provides an accurate equation of state for realistic models of hard n-alkane molecules. An empirical formula describing the EOS of repulsive n-alkane chains is given.