Heat capacity is an important and fundamental thermodynamic parameter in materials. The temperature-dependent heat capacity (HC) was studied extensively. Here, the universal correlation between the experimental heat capacity Cp and the coefficient of thermal expansion β in reference solids at high temperatures: Cp = Co + Eβ (C0 and E: constants) and the volume-dependent heat capacity CTE in the temperature range from several Kelvins to melting temperatures is quantitatively determined: CTE = Eβ, and a new phenomenological model of the experimental heat capacity below the melting temperature in the volume dimension is established: Cp = CT + CTE (the non-volume-dependent heat capacity CT = C0fD, fD: Debye function). Previous harmonic and anharmonic HC models explain the HC at low temperatures and high temperatures, respectively. The new model successfully explains the HC at the whole temperature range below the melting temperature and quantitatively determines the change behavior of the temperature and volume in solids after absorbing the heat.