The algorithms for calculation of densities from Sanchez-Lacombe (S-L) and group-contribution latticefluid (GCLF) equations of state have been put forward, respectively. From the S-L equation of state the relationship between the equation characteristic parameters and critical properties was deduced, and the influence of molecular weight of the polymers on critical properties was investigated. However, for the GCLF equation of state, it was surprising to find that there as many as four roots were found at a saturation temperature and pressure for gases, while still two roots above the critical temperature. For polymers, only two roots could be found. So the formerly accepted consistency between the magnitude of the density and vapor or liquid phase is not applicable yet. A way about how to identify the root and corresponding phase was suggested.