Volume parameters for room-temperature ionic liquids (RTILs) and salts were developed. For 59 of the most common imidazolium, pyridinium, pyrrolidinium, tetralkylammonium, and phosphonium-based RTILs, the mean absolute deviation (MAD) of the densities is 0.007 g cm(-3); for 35 imidazolium-based room-temperature salts, the MAD is 0.020 g cm(-3); and for 150 energetic salts, the MAD is 0.035 g cm(-3). The experimental density (Y) for an alkylated imidazolium or pyridinium-based room-temperature ionic liquid is approximately proportional to its calculated density (X) in the solid state: Y = 0.948X - 0.110 (correlation coefficient: R-2 = 0.998, for BF4-, PF6-, NTf2--containing ionic liquids); Y = 0.934X - 0.070 (correlation coefficient: R-2 = 0.999, for OTf (-), CF3CO2-, N(CN)(2)(-)-containing ionic liquids).