Single-ion standard entropies, S-ion degrees, are additive values for estimation of the room-temperature (298 K) entropies of ionic solids. They may be used for inferring the entropies of ionic solids for which values are unavailable and for checking reported values, thus complementing the independent method of estimation from molar volumes (termed volume-based thermodynamics). Current single-anion entropies depend on the charge of the countercation, and so are difficult to apply to complex materials, such as minerals. The analysis of reported data here presented provides a self-consistent set of entropies for cations and charge-independent values for anions. Although the S-ion degrees values presented encompass only a limited set of ions, the retrieval of values for ions not listed is straightforward and is described. An unexpected and significant observation is that cation entropies are related to the molar volumes of the corresponding (neutral) condensed-phase metals.