The heat capacities of nine room-temperature ionic liquids (ILs) were measured in an adiabatic calorimeter. The obtained results were compared with the literature data. It was demonstrated that in most works the uncertainty of the heat capacity measurements for ILs is underestimated, and the possible causes of this were discussed. With the use of the set of 19 ILs for which the reliable heat capacity data and the density data are available, it was found that the quotient of heat capacity at constant pressure to volume for these liquids remains constant within +/- 5 % at a given temperature and linearly changes with temperature in the temperature range of (258 to 370) K. It was demonstrated that the selection of an IL for technical applications is limited not by its heat capacity but by the other parameters.